Police have fired tear gas and stun grenades at dozens of anti-government protesters who defied a ban on unauthorised demonstrations to march in the centre of the Bahraini capital.
Armoured security forces vehicles and riot police closed off some of Manama's main roads on Friday, but protesters still found ways to make it to the march, which had been called by the country's main opposition bloc al-Wefaq.
Protesters were calling for all "prisoners of conscience" being held by the government to be released.
The demonstrators, who came in small groups in the old quarter of the capital, were prevented from converging on a main road where they intended to march.
Some carried banners reading "Freedom for the prisoners" and "We want an independent judiciary", according to witnesses, who said Sheikh Ali Salman, the head of al-Wefaq was present.
Some also called for the downfall of the monarchy led by Hamad bin Isa al-Khalifa, the ruler of Bahrain.
The interior ministry said the protest was prohibited and that any participants were breaking the law.
Last week, a march attended by tens of thousands of demonstrators that had also been organised by al-Wefaq and other opposition groups had been approved by the authorities. It passed without incident.
On Tuesday, a Bahraini civilian court upheld jail sentences of between five and 25 years against leaders of last year's pro-democracy uprising, a decision that could fuel more unrest in the small Gulf Arab state.
Al-Wefaq condemned the ruling. Amnesty International, a US-based rights group, said that the verdicts showed "once more that the Bahraini authorities are not on the path of reform but seem rather driven by vindictiveness".
Opposition parties led by al-Wefaq are demanding full powers for the elected parliament to legislate and form governments.
Many of the country's citizens complain of being politically and economically marginalised based on their sect, a charge the government denies.
Bahrain, where the US Fifth Fleet is based, has been in political turmoil since a protest movement dominated by majority Shia Muslims erupted in February 2011 during a wave of revolts against authoritarian governments across the Arab world.
The Sunni Muslim ruling al-Khalifa family put down the uprising with martial law, troops from Saudi Arabia and other Gulf allies, but unrest has resumed, with almost daily clashes between protesters and police.
More than 50 people have been killed and hundreds arrested since the uprising began last year.