The discovery of a protester's body near the scene of clashes on Saturday threatened to tip Bahrain deeper into unrest as a 14-month-old uprising overshadows the return of the Formula One Grand Prix to the strategic Gulf kingdom.
Bahrain's Sunni rulers had pressed for the race to be held as a chance to rebuild their credibility on the world stage after it was called off last year as police and army troops cracked down on dissent.
Persistent protests, however, have left the monarchy struggling to keep attention on Sunday's Formula One race _ Bahrain's premier international event _ as the country's Shiite majority pressed ahead with a campaign to break the near monopoly on power by the ruling Sunni dynasty, which has close ties to the West.
At least 50 people have died in the conflict since February 2011 in the longest-running street battles of the Arab Spring.
Protesters again took their grievances to the streets nationwide Saturday after opposition groups said that a man was killed the day before during clashes with security forces. A statement by the Interior Ministry said the man who died was identified as Salah Abbas Habib Musa, 36.
"Down, Down Hamad" and "We don't want Formula One," the protesters shouted in reference to King Hamad bin Isa Al Khalifa. Confrontations between police and anti-government protesters turned violent in the Shiite opposition stronghold of Diraz, northwest of Manama. Opposition supporters set tires ablaze and riot police fired tear gas to disperse them. No injuries were reported on Saturday.
Musa's body was found in an area west of the capital, Manama, where clashes broke out after a massive protest march Friday. Opposition factions said riot police and demonstrators were engaged in running skirmishes around Shakhura, a village about five miles (10 kilometers) west of the capital Manama that is known for its burial mounds dating back more than 5,000 years.
Musa's death threatened to sharply escalate tensions in the island nation, which is home to the U.S. Navy's 5th Fleet. Opposition leaders claimed Musa was targeted by the security forces because he was a prominent activist in the opposition February 14 movement, which has been the driving force of Bahrain's Shiite revolt.
Authorities opened an investigation in a bid to defuse tensions. The Interior Ministry said the case was "being treated as a homicide." It did not give a cause of death but said investigators found "a wound" on the left side of Musa's body.
After the announcement, thousands marched on a main highway leading out of the capital. The heavily guarded Bahrain International Circuit, where the F1 teams have practiced ahead of Sunday's race, was about 20 miles (15 kilometers) away from the demonstration.
Race drivers have mostly kept quiet about the controversy surrounding the Bahrain GP.
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 rights to the event.
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.
Bahrain's leaders lobbied hard to hold this year's event in efforts to portray stability and mend the country's international image despite almost daily and increasingly violent confrontations between security forces and protesters.
A tweet by Bahrain's foreign minister, Sheik Khalid bin Ahmed Al Khalifa, described a massive government-sanctioned opposition rally on Friday as "examples of freedom of speech and assembly."
"Life goes on," he added.
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.
Backed by international rights organizations, opposition groups had called for the sporting event to be canceled again, claiming that going ahead with the race in Bahrain would give international legitimacy to the monarchy and its crackdown.
Besides the deaths, hundreds have been detained and tried in secret at a special security court. Dozens have been convicted of anti-state crimes.
Eight prominent opposition figures have been sentenced to life in prison on charges of trying to overthrow the state, including rights activist Abdulhadi al-Khawaja, whose two-month and counting hunger strike has galvanized the Shiite resistance in the past weeks.
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 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.
Associated Press writer Barbara Surk in Dubai, United Arab Emirates contributed to this report.