Protesters disrupted traffic in the central business district of the Bahraini capital Manama yesterday as part of efforts to step up pressure ahead of weekend by-elections.
The demonstration was called by a youth group that was one of the main engines of a Shiite-led uprising halted by security forces earlier this year.
Using their vehicles, the protesters managed to force traffic to a slow crawl on main roads leading to central Manama for around three hours in the morning, amid a heavy police deployment, said activists and witnesses.
Matar Matar, a senior member of Al Wefaq, Bahrain's largest Shiite opposition group, said: "There was a strong participation in the peaceful movement."
Mr Matar distanced his group from the protest, however, saying it was organised by youth groups.
The February 14 youth group, which helped to organise the pro-reform protests this year, had used Facebook to arrange the demonstration yesterday.
The state news agency BNA said later roads had been "reopened" and that traffic was "normal", reporting police had to divert vehicles to ease "congestion".
The interior ministry had warned people from answering calls to protest, saying anyone caught hampering traffic would risk imprisonment and could have their driving licence revoked.
Mohammad Mascati, head of the Bahrain Youth Society for Human Rights, said: "There will be protests on Friday and Saturday and demonstrators will return to Pearl Square to call for political reforms, a constitutional monarchy and boycotting by-elections.
Tensions have been on the rise in the Gulf kingdom ahead of the elections scheduled to take place on Saturday.
Al Wefaq has already pulled out of the polls that were called to replace 18 of its MPs who walked out of the 40-member parliament in February in protest against the crackdown on demonstrators.
Authorities said 24 people have been killed during the uprisings, including four policemen. The opposition has puts the death toll at 30.