Security forces in Bahrain have fired tear gas and arrested protesters during marches in the traditional market area of the capital Manama, forcing many businesses to close.
The Interior Ministry said on Monday that it had made a "number" of arrests.
Among them was rights activist Yousef al-Muhafedha, the acting head of the Bahrain Centre for Human Rights, according to his wife, Zainab al-Sairafi.
Al-Muhafedha's arrest could stir more backlash, less than a week after a Bahraini court rejected an appeal to overturn the jail sentence of the rights centre's director, Nabeel Rajab.
The court cut one year from his three-year sentence on charges of encouraging "illegal gatherings" linked to the 22-month uprising against the kingdom's ruling system.
On Monday, authorities set up checkpoints and expanded patrols across Manama before rallies to mark an annual commemoration for two protesters killed in 1994.
Separate groups of hundreds of protesters chanted slogans in the narrow streets of the city's market district.
The protests are the latest attempt by Shia-led demonstrators to stage marches in the heart of the capital.
More than 55 people have been killed in unrest since February 2011, when Bahrain's majority Shia escalated their fight for a greater political voice in the Sunni-ruled kingdom.