Authorities in Bahrain have tightened security ahead of practice sessions for Sunday's Formula 1 Grand Prix.
Anti-government protesters have promised "three days of rage" to coincide with the event.
Correspondents say there is palpable unease about the fate of the race amid escalating unrest and violence.
On Wednesday night, Force India team members were forced to flee as petrol bombs were thrown near their car on their way back from the track.
The four mechanics in a 4x4 were caught in the middle of an incident as police clashed with protesters. Two members of the team have since asked to return home.
Formula 1's governing body, the FIA, only decided to go ahead with this weekend's race at the last minute.
Bahrain has seen protests against the ruling Sunni al-Khalifa clan for more than a year. Last year's F1 was cancelled after 35 people, including five police, were killed in demonstrations.
There has been pressure from activists outside and inside Bahrain for the lucrative event to be called off this year as well.
"Formula One in Bahrain has been taken as PR for the ruling elite, the repressive dictators who are ruling the country," said human rights activist Nabeel Rajab at a news conference.
Earlier in the week, Bahraini security forces fired stun grenades at protesters outside a cultural exhibition in Manama.
"A number of rioters and vandals had been arrested for taking part in illegal rallies and gatherings, blocking roads and endangering people's lives by attacking them with petrol bombs, iron rods and stones," the Information Affairs Authority said in a statement, citing Maj-Gen Tariq Al Hassan.
A local journalist told the BBC the demonstrators in Old Manama were shouting "Down, down, F1" and demanding the release of Abdulhadi al-Khawaja, an activist who has been on hunger strike in prison for more than two months.
Mr Khawaja is now said to be refusing everything except water.
Another protest has been called for 16:00 local time (14:00 GMT) outside the Bahrain International Circuit. Correspondents say riot police will have to show restraint with the international media so close at hand.
The BBC's Rupert Wingfield-Hayes in Manama says the protesters are determined to use the race to draw attention to their campaign, while the government is determined to stop them.
Bahrain's ruling royal family are being pressured to improve human rights and make reforms by the majority Shia population, who accuse the minority ruling Sunnis of discrimination.