Anti-government demonstrators have clashed with riot police in Bahrain's capital Manama as activists defied a ban on unauthorised protests.
Police fired tear gas and blocked roads in an effort to put down the protest.
Protesters from Bahrain's Shia Muslim majority have been demanding reforms from the ruling Sunni Muslim al-Khalifa family since last year.
Last week thousands of people took part in an approved protest, without incident.
Friday's protests were the latest attempt by Shia-led anti-government activists to revive an uprising which started in February 2011 and has so far killed 19 people.
Authorised protests in Bahrain, a small Gulf island state which hosts the fifth fleet of the US navy, have been held largely on the outskirts of the capital.
The latest demonstration was held in central Manama.
Police tried to block some roads using armoured vehicles to prevent demonstrators from reaching the march, Reuters reported.
The Bahraini government has tried to mollify protesters with some reforms and last year appointed a leading lawyer to assess the powerful crackdown on protesters last year.
The al-Khalifa family called in help from Saudi Arabia's military and the United Arab Emirates' police force to help quell demonstrations last year.
Earlier this week a court in Manama upheld prison sentences of between five and 25 years handed to some leading activists.