A Bahraini man was found dead today after clashes with riot police in the village of Shakhoura, one day before Bahrain's Formula One Grand Prix race, opposition party Wefaq said in a statement.
It named the man as Salah Abbas Habib and said the body of the man, in his 30s, was found on the roof of a building.
Wefaq said Mr Habib was part of a group who were beaten by police during the clashes, which happened late on Friday night.
A government official declined to comment.
A funeral march for Mr Habib will take place tomorrow, setting the stage for riots during the big race itself. Mr Habib's death will infuriate members of Bahrain's Shia Muslim majority, who complain they have long been marginalised by the Sunni ruling family and have been treated brutally since the crackdown on protests last year.
The uprising forced the cancellation of last year's Grand Prix, but this year the authorities were determined to stage it.
Organisers and sponsors have ignored calls from human rights groups for a boycott.
The head of Formula One's governing body was unrepentant today about the decision to race in Bahrain and said the sport would suffer no lasting damage to its image despite worldwide condemnation.
"I am sorry about what has been reported. I am not sure that all that has been reported corresponds to the reality of what is happening in this country," International Automobile Federation president Jean Todt told a small group of reporters at the Sakhir circuit ahead of tomorrow's race.
Thousands of demonstrators took to the streets in anti-government protests and activists reported clashes in several districts today.
Around 7,000 people took part in a march called by opposition parties in Diraz, holding banners for democratic
reforms in the Shia-majority Gulf Arab state, which is governed by the Sunni Muslim Al Khalifa family.
They held up a banner depicting Formula One race drivers as riot police beating up protesters. In al-Bilad al-Qadeem, a Shia neighbourhood of the capital Manama, police fired tear gas to stop several hundred protesters reaching a main road.
"They used rubber bullets, tear gas and sound bombs," said Mohammed al-Maskati of the Bahrain Youth Society for Human Rights. He said the march was held in protest against the death of Mr Habib.
Meanwhile, dozens of armoured vehicles were deployed along the main highway to Bahrain's Formula One Grand Prix circuit.
Security forces were stationed around the capital of Manama and along the road to the Bahrain International Circuit in Sakhir. Activists say barbed wire has been installed near some parts of the main highway.
"The government are using the Formula One race to serve their PR campaign," said rights activist Nabeel Rajab. "It's not turning out the way they wanted."
The cars take to the track again today for practice and qualifying sessions."They need to fix the country first, then they can start looking at Formula One and other events," said Umm Hussein, one of 10,000 demonstrators who gathered near the capital, Manama, yesterday.
While sports journalists poured in to cover the race, non-sports reporters from Reuters and some other news organisations have not been granted visas to visit the Gulf island, which in 2004 became the first country in the region to host Formula One.
Hackers brought down the F1 website intermittently yesterday and defaced another site, f1-racers.net, to support what they described as the Bahraini people's struggle against oppression.
Reuters