MANAMA, Bahrain — Security forces in Bahrain set up checkpoints and stationed armored vehicles in anti-government strongholds Sunday to confront possible protests coinciding with the Gulf nation's Formula One Grand Prix.
The beefed-up security moved into place shortly before the start of the race, which was being held after a series of clashes and protest marches by opposition groups angered by Formula One's return to the kingdom. Protesters claim at least one person was killed by riot police in the run-up to the event.
At least 50 people have been killed since unrest erupted in Bahrain in February 2011 in the longest-running street battles of the Arab Spring.
Last year's F1 race — the nation's premier international event — was canceled because of the uprising by the kingdom's Shiite majority, which is seeking to break the ruling Sunni dynasty's hold on power. Opposition groups have sharply criticized the return of the race to the strategic island nation, which is home to the U.S. Navy's 5th Fleet.
Bahrain's rulers had pushed hard for F1 organizers to restore the race. But the worldwide spotlight also has put the leadership in a difficult spot as scenes of clashes and a massive protest march have often overshadowed the preliminary events on the track.
The unrest, however, has remained far from the Formula One's desert circuit about 35 kilometers (20 miles) southwest of the capital Manama.
On Saturday, opposition groups claimed a man — 36-year-old Salah Abbas Habib Musa — was killed by riot police and his body left on a rooftop. The Interior Ministry said the death is being treated as a "homicide" and promised an investigation, but have given few other details.
Meanwhile, authorities have tried to dismiss claims that a prominent jailed activist — on a hunger strike for more than two months — is in sharply failing health.
Race drivers have mostly kept quiet about the controversy surrounding the Bahrain Grand Prix. Asked about Musa's death after taking pole position in Saturday's qualifier, F1 world champion Sebastian Vettel said, "I think it's always dreadful if someone dies."
Bahrain's monarchy is the main backer of the F1 race, and the crown prince owns the rights to the event.
Shiites account for about 70 percent of Bahrain's population of just over half a million people, but claim they face widespread discrimination and lack opportunities granted to the Sunni minority. The country's leaders have offered some reforms, but the opposition says they fall short of Shiite demands for a greater voice in the country's affairs and an elected government.
The unrest also has put Washington into an awkward position. U.S. officials have called for efforts to reopen political dialogue in Bahrain, but are careful not to press too hard against the nation's leadership and possibly jeopardize its important military ties.
The hacker group Anonymous, which last week took down the official Formula One website in protest over the race, on Sunday posted what it said was personal data about dozens of race ticket holders stolen from Formula One servers.
The spectator information was partially redacted before being posted. It included customers' last names, and partial phone numbers and email addresses. The authenticity of the information could not immediately be verified.
In a statement posted online, the hacker group threatened further attacks should any harm come to hunger strike Abdulhadi al-Khawaja or his family, saying, "Anonymous will respond with fury and rage the likes of which have never been seen."
The group criticized the Bahraini government for what it said was "an attempt to conceal the oppression it is committing against its own people." It also blasted Formula One for supporting the government's hosting of the race, saying revenues generated is being used to buy tear gas and ammunition used against demonstrators.
Anonymous last week took responsibility for a denial-of-service attack against the official Formula One website and another site, F1-racers.net.
Denial-of-service attacks work by flooding a website with traffic.
As the race got under way, the official Formula One site was operating as normal. However, the content of F1-racers.net was replaced with a video clip showing footage of Bahraini police clashing with protesters and an apparently new message that included today's date and the list of hacked ticket information.
Bahrain was the first Middle Eastern country to welcome F1 in 2004. Members of the ruling Al Khalifa dynasty are huge fans of the sport and the country's sovereign wealth fund, Mumtalakat, owns 50 percent of leading team McLaren.
The rulers have billed the F1 race as an event that will put the divided society on the path of reconciliation. They vowed zero tolerance for unrest and repeatedly warned the opposition against sabotaging Bahrain's racing weekend, which will draw a worldwide TV audience of about 100 million in 187 countries.
AP Business Writer Adam Schreck in Dubai, United Arab Emirates, contributed to this report.