Bahraini security forces have fired teargas and stun grenades at protesters gathered ahead of the first anniversary of pro-democracy demonstrations.
Protesters tried to gain control of the Pearl roundabout in the capital, Manama - the focal point of protests last year.
Thousands of riot police and other security forces have been deployed across the kingdom.
At least 60 people have died since the Shia-led protests began last February.
Demonstrators on Monday evening advanced about 2km (1.5 miles) on Pearl roundabout before they were pushed back by teargas and rubber bullets, Reuters reports.
"We will not back down,'" said Nader Abdulimam, who sought shelter in a house with other protesters to get away from the tear gas.
"This has gone on for one year and it will go for another year or more.''
The demonstrators, who are from the Shia majority, are demanding a constutional monarchy in Bahrain.
The government of King Hamad bin Isa al-Khalifa says it is meeting its commitments to introduce political reforms, correspondents say.
But the opposition, as well as human rights groups, say little is being done to curb the police.
An independent inquiry was set up by King Hamad after growing international condemnation of human rights abuses. In a report in November, it confirmed excessive use of force and systematic torture of prisoners in detention by security forces.
Last February, protesters occupied the square for a month and were only driven out after neighbouring Saudi Arabia and other Sunni-ruled Gulf states dispatched troops to Bahrain to help clear it.