ISLAMABAD (Reuters) - Toppled in a 1999 military coup, jailed and exiled, Pakistan's Nawaz Sharif has made a triumphant election comeback and looks set to form a stable government capable of implementing reforms needed to rescue the fragile economy.

Sharif may not win enough seats to rule on his own but has built up enough momentum to avoid having to form a coalition with his main rivals, former cricketer Imran Khan's Tehrik-i-Insaf (PTI) and the Pakistan People's Party (PPP).

The steel magnate held off a challenge from Khan, who had hoped to break decades of dominance by Sharif's Pakistan Muslim League (PML-N) and the PPP, led by the Bhutto family.

The two parties have formed governments whenever the military, the most powerful institution in the nuclear-armed nation, has allowed civilian rule.

U.S. President Barack Obama congratulated Pakistanis for the successful election and said the United States would work with the new government as an equal partner.

"By conducting competitive campaigns, freely exercising your democratic rights, and persevering despite intimidation by violent extremists, you have affirmed a commitment to democratic rule that will be critical to achieving peace and prosperity for all Pakistanis for years to come," Obama said in a statement.

But facing Islamist militant violence, endemic corruption, chronic power cuts and crumbling infrastructure, even Sharif has described Pakistan as a "mess".

Khan put up a strong fight and he is likely to remain a force in politics, possibly becoming the main opposition figure. The PPP, which led the government for the last five years, has done badly and could come in third place.

Television channels said of the results declared by Sunday evening, Sharif's PML-N had captured 94 of the 272 contested National Assembly seats.

Based on trends, it was likely to get around 130, and should easily be able to make up the required majority of 137 with support from independents and small parties.

The PTI has secured 21 seats while the PPP won 19.

The elections, held on Saturday, were marred by a campaign by Islamists to block the voting. Despite pre-poll violence and attacks that killed at least 40 people, voter turnout was a robust 60 percent.

Once it establishes a majority, Sharif's party would be allocated a majority of 70 other parliamentary seats that are reserved for women and non-Muslim minorities.

Sharif has waited patiently to rule Pakistan again. As the main opposition leader, he avoided undermining the PPP when it was in trouble, and analysts describe him as more cautious than when he was prime minister twice in the 1990s.

"Seemingly a genuinely changed man from his troubling stints as prime minister in the 90s, Sharif now appears to have both a genuine mandate as well as a grasp of the direction Pakistan needs to be steered in," said political analyst Cyril Almeida.

In one sense, the polls were a democratic landmark, marking the first time one elected government was to replace another in a country vulnerable to military takeovers.

But Saturday's vote failed to realise the hopes of many that the hold of patronage-based parties would end after years of misrule and corruption.

Sharif, 63, is almost certain to become prime minister for a third time. The religious conservative has said the army, which has ruled the country for more than half of its turbulent 66-year history, should stay out of politics.

But he will have to work with Pakistan's generals, who set foreign and security policy and will manage the country's thorny relationship with the United States as NATO troops withdraw from neighboring Afghanistan in 2014.

Sharif also believes Pakistan should reconsider its support for the U.S. war on Islamist militancy, which has earned the country billions of dollars in aid.

REFORMER

Sharif, who advocates free-market economics, is likely to pursue privatization and deregulation to revive flagging growth. He has said Pakistan should stand on its own two feet but may need to seek a another bailout from the International Monetary Fund to avoid a balance of payments crisis.

The PML-N leader has said he could do business with the IMF, meaning he may be open to reforms like an easing of subsidies and a widening of Pakistan's tiny tax base to secure billions of dollars from the global lender.

"A better-than-expected result for Nawaz could prove to be an albatross around his neck," said Muhammad Malick, a popular current affairs broadcaster.

"With an overwhelming majority of seats and without needing the crutch of coalition partners to form government, he will have fewer excuses for failure on key policy issues such as the economy and terrorism."

In a reminder of the security challenges that Sharif will face, a blast on a bus in the tribal area of North Waziristan killed 19 people on Sunday, security officials said.

Sharif will likely press for negotiation with the Pakistan wing of the Taliban, whose bombing attacks failed to derail the election, but he could run into resistance from the military which has lost thousands of soldiers fighting the insurgency.

Despite Pakistan's history of coups, the army stayed out of politics during the five years of the last government and threw its support behind the election.

However, some fear the military could step back in if there were a repeat of the incompetence and corruption that frustrated many Pakistanis during the last government's rule.

In the end, cricketing hero Khan did not have the momentum needed to trip up Sharif despite his popularity among urban youths, many of whom were voting for the first time.

They had rallied behind Khan's calls for an end to graft and a halt to U.S. drone strikes against suspected militants on Pakistani soil, widely seen as a violation of sovereignty.

In a video message, Khan said the election would boost Pakistan's young democracy, but added his party was collecting evidence of what he said was vote-rigging.

"We are now moving towards democracy. I congratulate the nation on the numbers in which they turned out to vote. The youth was with me. That is my victory," he said.

(Additional reporting by Mehreen Zahra-Malik and Katharine Houreld in ISLAMABAD, Gul Yousafzai in QUETTA, Mubasher Bukhari in LAHORE and Jibran Ahmed in PESHAWAR; Writing by Michael Georgy; Editing by Raju Gopalakrishnan and Jon Hemming)

LONDON (Reuters) - Olympiakos Piraeus defeated Real Madrid 100-88 with a dominant second half display on Sunday to win Europe's premier basketball trophy for the second year running.

Inspired by a vocal travelling support who defied Greece's economic problems to make the trip to London, Olympiacos battled back from 27-10 down after the first quarter of the Euroleague final to take the lead early in the second half.

They rarely looked threatened, shooting 39 points in the fourth quarter to clinch their third Euroleague title 100-88.

"(Madrid) scored some incredible shots in the first quarter, but we put a stop to that and started rebounding offensively, and I think that was the key to success in the end," said Olympiakos forward Pero Antic.

The win was in a stark contrast to last year when it took a game-winning shot from Georgios Printezis at the buzzer to overcome CSKA Moscow.

Having defeated much-fancied CSKA again in Friday's semi-final, the Greeks started slowly on Sunday and struggled against Madrid's sharp shooting in the first quarter.

But Olympiakos' trademark ironclad defence soon kicked in, allowing eight-times champions Madrid just 14 points in the second quarter and 20 in the third as Kyle Hines and Pero muscled out the Spanish forwards inside the paint.

The team's talisman Vassilis Spanoulis dominated the second half, shooting a total of five three-pointers and notching up four assists. He was voted the Final Four's most valuable player for the third time and finished top scorer with 22 points.

"It has been a very difficult year - you know our budget," Spanoulis said. "Our backs have been against the wall many times, but we have stayed together and fought back each time."

A 21-point haul for Rudy Fernandez, who quit the National Basketball Association to return to Madrid last year, could do little to stem the tide.

"Spanoulis' three pointers changed the game's rhythm while we were still working to get back into the game, but in the end they were able to control the (lead)," said Real coach Pablo Laso.

Earlier, Barcelona's Marcelinho Huertas missed a potentially game-winning shot at the buzzer, letting CSKA hold on for a 74-73 victory in the league's third place playoff.

(Writing by Patrick Graham; Editing by John Mehaffey)

At the conclusion of a two-day meeting of leading financial representatives from the G-7 countries the U.S., Germany, France, Italy, Japan, Canada and the U.K. host British Treasury chief George Osborne said there was a formal acknowledgement that each member needed to secure their own countries' growth by balancing austerity measures with growth-enhancing policies.The officials also agreed on the importance of finding measures to deal with failing banks and working collectively to stop companies and individuals from dodging their tax bills.

The global recovery from recession over the past few years has been patchy. While the U.S. economy, the world's largest, appears to be gaining traction, many European countries are in recession as they try to get a grip on their public finances through deep spending cuts and tax increases.

"The will is still there to reduce the deficits but there is certainly a change of tone," said Pierre Moscovici, France's finance minister at the conclusion of the two-day summit at a country house around 50 miles (80 kilometers) northwest of London.

Japan, the world's number 3 economy has been in focus in recent months. The new government of Prime Minister Shinzo Abe has promised aggressive steps to restart the country's postwar boom, which effectively ground to a halt in the early 1990s. As part of that effort, the Bank of Japan plans to double the amount of cash circulating in the Japanese economy and held as bank reserves.

One of the offshoots of the policies has been a dramatic fall in the value of the yen. On Thursday, the dollar rose above 100 yen for the first time in over four years. The yen has weakened by more than 20 percent against the dollar since October, when it was trading at around 78 yen.

As well as potentially boosting economic growth by making its exports more competitive, the flipside of a lower yen is that it can also stoke inflation by increasing the price of imports. For a country that's seen prices fall for much of the past 15 years, that's important.

The rapid slide in the value of the yen has sparked fears of a "currency war" where countries use their exchange rates as an economic weapon. If other countries respond to the falling yen by debasing their currencies, Japan will be back at square one and the world economy could suffer. Sharp fluctuations in the value of currencies can hurt business confidence and investment.

So far, the argument presented by Japanese officials that it has been targeting monetary stimulus and not its exchange rate has been accepted by Japan's G-7 partners.

Osborne, who hosted the two days of informal discussions, said the G-7 countries agreed to make sure that "policies are oriented towards domestic objectives."

In a rare development, the G-7 didn't actually issue a communique at the conclusion of its deliberations. However, Osborne said the previous communique "was a successful statement and one that has been held to" a clear reference to Japan.

In February, when markets were particularly roiled by developments in Japan, the G-7 said their respective fiscal and monetary policies were oriented toward meeting domestic requirements and that exchange rates were not a target of policy.

A senior U.S. Treasury official, speaking on condition of anonymity, said there was a good discussion about what's going on in Japan and that Japanese officials went into some detail about how the new policy was helping to boost domestic demand.

The official reaffirmed the importance that Japan continues to meet previous commitments, a point made a day earlier by Treasury Secretary Jacob Lew who said he was monitoring developments.

Analysts said it's difficult for the G-7 to make any concerns over Japan public because other countries, such as the U.S. and Britain, have been accused of debasing their respective currencies over the past few years through their monetary stimulus programs.

"It's a bit like the pot calling the kettle black," said Simon Derrick, senior currency strategist at BNY Mellon.

All participants at the meeting said boosting economic growth was a priority now that financial markets appear to have calmed down, especially with regard to the debt crisis that has gripped the 17-country Eurozone.

Bad banking practices around many parts of the world were behind the financial explosion in 2008, which sent the world economy skidding to its deepest recession since World War II. Britain's Osborne said it was important to swiftly complete work to make sure that no bank is too big to fail.

"We must put regimes in place ... to deal with failing banks and to protect taxpayers and to do so in a globally consistent manner," he said.

Mario Draghi, the president of the European Central Bank, said the bank was working out what it can do to make sure banks lend more. Though banks have managed to reduce their debt and bolster their capital reserves and have benefited from liquidity offers from the ECB, lending remains stuck at relatively low levels particularly to smaller and medium sized enterprises.

"There wasn't any call to do more really," Draghi said, a day after Britain's Osborne indicated there would be discussions on the role of the world's central banks in shoring up global growth.

Osborne also said it was important to tackle tax avoidance and evasion, and said some of the U.K.'s offshore dependencies are working to make sure they follow the spirit of new international standards.

"Today, we all agree on the importance of collective action to tackle tax avoidance and evasion," he said. "We are absolutely determined to make progress this year .... It is vital that both developed and developing countries collect the tax that is due to them."

The American Heart Association (AHA) issued a scientific statement on Thursday saying owning a pet may help to decrease a person's risk of suffering from heart disease and is linked with lower levels of obesity, blood pressure and cholesterol.

"Pet ownership, particularly dog ownership, is probably associated with a decreased risk of heart disease," Glenn N. Levine, a professor at Baylor College of Medicine in Houston, said in a statement.

A study of more than 5,200 adults, cited by the AHA, showed dog owners were more physically active than non-owners because they walk their pets. Other research has revealed the calming effects of pets, which are used in animal-assisted therapy programs.

Levine, the chairman of the committee that wrote the statement published online in the journal Circulation, added that the benefits are clear on cutting the risk factors for heart disease. But the studies are not definitive or prove that owning a pet directly causes a reduction in heart disease risk.

"What's less clear is whether the act of adopting or acquiring a pet could lead to a reduction in cardiovascular risk in those with pre-existing disease," he said, adding more research is needed.

About 78.2 million people in the United States own a dog and 86.4 million have a cat, according to figures from the American Pet Product Association 2011-2012 National Pet Owners Survey.

Research has shown that the loyalty and love pets display can reduce stress, anxiety, depression and loneliness in their owners and increase their sense of well-being and self-esteem.

(Reporting by Patricia Reaney; Editing by Marguerita Choy)

David Thatcher, 91, charms admiring World War II history buffs with detailed accounts of his part in the 1942 Doolittle Raid on Tokyo, in which he earned a Silver Star.

Retired Lt. Col. Edward Saylor, 93, still gets loud laughs from crowds for his one liners about the historic bombing raid 71 years ago Thursday that helped to boost a wounded nation's morale in the aftermath of Japan's attack on Pearl Harbor.

Cole, Thatcher and Saylor three of the four surviving crew members from the history-making bombing run are at Eglin Air Force Base in the Florida Panhandle for a final public reunion of the Doolittle Raiders. They decided to meet at Eglin because it is where they trained for their top-secret mission in the winter of 1942, just weeks after the Japanese devastated the American fleet at Pearl Harbor.

The fourth surviving raider, 93-year-old Robert Hite, could not make the event.

"At the time of the raid, you know the war was on and it was just a mission we went on, we were lucky enough to survive it but it didn't seem like that big of a deal at the time. I spent the rest of the war in Europe and with the guys in Normandy and taking bodies out of airplanes and stuff and I didn't feel like a hero," Saylor said Wednesday following a ceremony in which an F-35 Joint Strike Fighter maintenance hangar at the base was named in his honor.

Saylor joked with the audience of young airmen and local dignitaries.

"My reaction when I out found out we were bombing Japan from an aircraft carrier was that it was too far to swim back home so we might as well go ahead with it," he said.

The 16 planes, loaded with one-ton bombs, took off from the aircraft carrier on less than 500 feet of runway. They had only enough fuel to drop their bombs and try to land in China with the hope that the Chinese would help them to safety.

"We were all pretty upbeat about it, we didn't have any bad thoughts about what was going to happen. We just did what we had to do," said Cole, who was Doolittle's co-pilot.

Wednesday's event at the base is part of a weeklong series of activities planned by the military and community leaders to honor the men.

Thomas Casey, business manager for the Raiders and a longtime fan of the men, said the four survivors have decided they can no longer keep up with the demands of group public appearances.

"The mission ends here in Fort Walton Beach on Saturday night, but their legacy starts then," he said.

Casey said he hopes everyone who has had a chance to interact with the men will keep their legacy alive. "I want them to tell the story to their children, their grandchildren, their neighbors and keep their story going because their story is worthwhile telling."

At each reunion is a case containing 80 silver goblets with the name of each raider inscribed right-side up and upside down on a single goblet. The men toast their fallen comrades each year and turn their goblets upside down in their honor.

They have also saved a bottle of Hennessy cognac from 1896, the year mission commander James Doolittle was born. The Raiders had said the final two survivors would open the bottle, but they have since decided that the four survivors will meet in private later this year for the toast.

At Wednesday's dedication of the Saylor Hangar, the three men posed for pictures beneath a vintage B-25 bomber and an F-35 Joint Strike Fighter that sat beside it.

Col. Andrew Toth, commander of the F-35 squadron at Eglin, told the men, "You boosted the morale of this nation just four months after Pearl Harbor. Thank you for your dedication and service."

Young airmen and women obtained the old veterans' autographs and thanked them for their service.

"I've seen the movies you know, 'Thirty Seconds Over Tokyo,'" said Air Force Lt. Col. Mike Matesick. "I think this is awesome because they actually trained here at Eglin and they did the ceremony to actually name a hangar after one of the guys. It's pretty cool."

Larry Kelley owns the vintage B-25 aircraft that Cole flew a day earlier during a demonstration of four restored B-25s from the World War II era.

Kelley choked up when trying to explain what it has meant to him to meet Cole and the other raiders over the past several years and to have the men fly in his aircraft.

"Here are some of the most famous aviators that came out of World War II and they've never put a nickel in their pocket" as a result of their fame, he said. Instead, he said, any money from book signings and appearances has always gone to the James H. Doolittle Scholarship Fund for aviation students.

Kelley said sitting beside Cole while Cole took the controls of the B-25 and landed the aircraft was a highlight of his life as a World War II and aviation buff.

"Oh yeah, he did most of the flying today. He did the landing. He's dead on. I kept looking over the altimeter. I told him to hold 1,500 feet and I kept looking at the altimeter and it was dead on: not 1,499 feet, not 1,501 feet. He had the altimeter pegged at 1,500 feet," he said.

Headline earnings for the first three months of the year came in at 4 U.S. cents a share from a restated 12 U.S. cents a share in the previous quarter. Production slumped 11 percent to 477,000 ounces.

Gold Fields unbundled its mature deep-level KDC and Beatrix operations in South Africa into a separately listed company, Sibanye Gold, earlier this year.

These labour-intensive operations were also rocked last year by the wave of wildcat strikes that hit the country's mining sector.

Lower group production allowed notional cash expenditure, which includes capital expenditure, to decrease by 2 percent to $1,291 an ounce in the March quarter.

The spot gold price declined 5 percent in the quarter but has fallen a further 12 percent since the end of March, which will put pressure on margins.

Gold Fields is targeting full year production of between 1.8 and 1.9 million ounces.

The market has not embraced the split with the warmth Gold Fields had hoped and its share price is down over 30 percent so far this year.

LOS ANGELES (AP) -- Sometimes you just can't wait for Comic-Con whether you're a fan or a filmmaker.

With the summer movie season now beginning in early May ("Iron Man 3" opens Friday), studios are co-opting the July pop-culture convention's model of stoking interest in anticipated films by bringing sneak-peeks of new material directly to super fans, who then, it is hoped, spread their enthusiasm via word-of-mouth and social media.

For "Star Trek: Into Darkness," which opens May 17, Paramount shared early photos and videos with Trekkies devoted enough to download an iPhone or Android app. Other aspiring blockbusters, including Disney's "The Lone Ranger" and Sony's "Elysium," were subjects of their own individual Comic-Con-style events recently: Studios invited fans to local theaters, where they heard directly from the films' stars and were the first to see the action-packed trailers and other select scenes.

Johnny Depp and Armie Hammer took questions from fans at "The Lone Ranger" event in Las Vegas in a segment streamed live online. Matt Damon and "District 9" writer-director Neill Blomkamp participated in the "Elyisum" showcase, held simultaneously in theaters in Los Angeles and Berlin. Only those who regularly follow the films online find out about such special events.

Studios value the approach because it allows them to reward devoted fans while building early buzz for their films. It also circumvents, in a way, the more traditional method of staging promotional events for entertainment media and then depending on those outlets to spread the news to fans.

There are no better ambassadors to get word-of-mouth going," said Marc Weinstock, Sony's co-president of worldwide marketing. "Movies are such a viral thing."

Asad Ayaz, senior vice president of marketing for Disney, said one aim of "The Lone Ranger" Las Vegas event last month was to generate as much international interest as possible in the film's trailer, which made its public debut there. Fans from as far away as China submitted questions for Depp, Hammer, director Gore Verbinski and producer Jerry Bruckheimer via Twitter during the online broadcast.

One wanted to know what other characters Depp wants to play.

"Carol Channing," the actor said. "I mean that. She's fantastic... Another guy that I would love to do the life story of is Don Rickles, which I don't know if he's well-known in China."

Such starry mini-screenings can help raise a film's social-media profile in the crowded summer marketplace, Ayaz said.

"When we did our event for 'The Lone Ranger,' 'Lone Ranger' was trending on Twitter worldwide and in the U.S. for several hours during and after the event, and that's because of fans tweeting," he said. "It's all about getting eyeballs on our trailer and getting people to see this amazing film, so the social-media aspect just makes it. It's a giant halo and it spreads the word."

"The Lone Ranger" opens July 3.

Weinstock said the positive Twitter response to the "Elysium" event was just what the studio had hoped for.

The film's writer-director, though, confessed that he'd rather keep its content under wraps until the movie opens in August, but that's not the way the marketplace works.

"I try to show as little as I can," Blomkamp told reporters after the fan screening. "The thing is, if you're a responsible, functioning filmmaker in the 21st century, you can't spend $100 million and then try to behave as though you're going to wrap it under a blanket... Rationally, I understand that people have to get to know about the film and word has to get out there. Personally, I don't really like it."

Not all film marketing experts are sold on the ultimate value of fan events. Ben Carlson, president of market tracking firm Fizziology, believes the biggest social-media boost still comes from online trailer releases.

"As soon as you put a good trailer out, it almost immediately becomes a trending topic on Twitter," he said, adding that in-person showcases like those held by Disney and Sony don't have the same social media impact.

"It's more for the influential film bloggers. It does some nice heavy-lifting there," he said. "I don't think the mainstream moviegoer who might be in Kansas City or Memphis or Helena, Mont., is going to necessarily be paying attention to what's happening at an event with a few thousand people, but they will read about it on Ain't It Cool News."

Carlson said the trailer for another anticipated summer release, Guillermo del Toro's "Pacific Rim," premiered for a group of fans before making its online debut, and it was the latter that resulted in a palpable Twitter bump.

"Instantly thousands and thousands of people were talking about it, and that's without any kind of special push to it at all," he said. "People just love the content."

Still, in a hyper-saturated media world, there's something about being the first to see something really cool, never mind seeing movie stars like Depp and Damon in person. Disney's Ayaz said he expects the studio to hold fan-focused events for future "tent pole" releases such as "Thor," ''Captain America" and "Maleficent." Sony previously held an event for "The Amazing Spider-Man," and is releasing the sequel next year.

"People are more distracted than ever before and they have a lot of different mediums to get access to our content, and what is more basic and more powerful than having a live event where you have your creative (people) the actual filmmakers and the actors and the talent from your film directly answering questions and showing their work to the fans?" Ayaz said. "It's a basic idea but it's still one of the most powerful ideas when you've got the goods and you've got a really good movie."

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Follow AP Entertainment Writer Sandy Cohen on Twitter: www.twitter.com/APSandy .

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Online:

The Lone Ranger: http://disney.go.com/the-lone-ranger/

Elysium:http://www.itsbetterupthere.com/site/

Star Trek: Into Darkness: http://www.startrekmovie.com/

Pacific Rim: http://www.pacificrimmovie.net/

Among the deaths, two occurred in the eastern province of Jiangsu; one was from eastern Zhejiang; while another was from central Anhui, based on a Reuters analysis of the data provided by Chinese health authorities on Monday.

The government did not provide more details of the victims.

Chinese health authorities said two new infections were reported in the eastern coastal province of Fujian. The virus, which was mostly concentrated in the region around the commercial capital of Shanghai, spread to Fujian in late April.

The Geneva-based World Health Organization (WHO) has said it has no evidence that the new strain of bird flu, which was first detected in patients in China in March, is easily transmissible between humans.

Chinese scientists have confirmed that the H7N9 strain has been transmitted to humans from chickens. But the WHO has said 40 percent of people infected with H7N9 appear to have had no contact with poultry.

The head of the U.S. Centers for Disease Control and Prevention said the current strain of bird flu cannot spark a pandemic in its current form - but he added that there is no guarantee it will not mutate and cause a serious pandemic.

(Reporting by Sui-Lee Wee; Editing by Michael Perry)

Network NBC said on Monday that Green, a former judge on the popular contest, is slated to perform his new song "Only You." Rock and Roll Hall of Fame inductee Stewart will perform material from his upcoming album, "Time," his first release of original material in over a decade.

Stewart and Green will perform on the May 8 episode, while Grammy-winning country-pop trio Lady Antebellum will promote their forthcoming album "Golden" on the May 14 episode.

Pop singer Robin Thicke, singer-producer Pharrell Williams and rapper T.I. will all perform on the May 14 episode of "The Voice," which averages about 14 million viewers over its two weekly shows.

The competition's fourth season, which installed pop singers Shakira and Usher to replace Green and Christina Aguilera as judges, reaches its climax in June, when one of the aspiring contestants will be proclaimed the winner and get a recording contract.

(Reporting by Eric Kelsey. Editing by Jill Serjeant and Andre Grenon)

The company hasn't said what it plans to reveal during the event at its Menlo Park, Calif., headquarters, but speculation has centered on a mobile phone made by HTC Corp. According to media reports, the phone would deeply integrate Facebook into the Android operating system, aiding Facebook in its aim to evolve from its Web-based roots into a "mobile-first" company.

"What Facebook wants is to put itself at the front of the Android user experience for as many Facebook users as possible and make Facebook more elemental to their customers' experience," said Forrester analyst Charles Golvin.

The move could help to attract more mobile advertisers. Though mobile ads were a big concern for Facebook's investors even before the company's initial public offering last May, some of the worry has subsided as the company muscles its way into the market.

Last year, Facebook began showing ads to its mobile audience by shoehorning corporate-sponsored content into users' news feeds, which also include updates from friends and brands they follow. Facebook now faces the challenge of showing people mobile ads without annoying or alienating them.

The mobile advertising market is growing quickly, thanks in large part to Facebook and Twitter, which also entered the space in 2012. Research firm eMarketer expects U.S. mobile ad spending to grow 77 percent this year to $7.29 billion, from $4.11 billion last year.

EMarketer said Wednesday that it expects Facebook Inc. to reap $965 million in U.S. mobile ad revenue in 2013. That's about 2.5 times the $391 million in 2012, the first year that Facebook started showing mobile ads.

Clark Fredricksen, vice president at eMarketer, said it's "tough to speculate" how much effect Thursday's announcement would have on ad revenue.

At the same time, he says "there are some clear reasons why a deeper integration with mobile operating systems and handsets make sense for Facebook. At the end of the day, the more deeply Facebook can engage consumers, no matter what device or operating system or handset," the better.

Such deeper integration could mean Facebook is no longer a stand-alone mobile app but part of the operating system's building blocks. For example, if users who want to take a photo would use Facebook's camera app. If they want to chat, they'd use Facebook's chat service. The invitation to the event, "come see our new home on Android," suggests that Facebook will be prominently featured on a phone's home screen.

Facebook's rival, Google Inc., makes the Android software that Facebook and HTC would be using under the widely speculated scenario. Google makes the software available on an open-source basis, meaning others including rivals are free to adapt it to their needs. Amazon.com Inc. does just that in modifying Android to run its Kindle tablet computers.

Facebook is No. 2 behind Google Inc. when it comes to mobile ads, and it isn't expected to surpass the online search leader any time soon. Google dominates the mobile search market with 93 percent of U.S. mobile search advertising dollars, according to eMarketer. Online music service Pandora Inc. is in third place when it comes to mobile ad dollars, followed by Twitter.