A teenager has been killed in street clashes between security forces and anti-government protesters in Bahrain.
Tension was high on the second anniversary of the uprising in the Gulf nation, activists said.
The demonstrators also included groups chanting against talks aimed at easing the Arab Spring-inspired unrest in the country, showing the deep divisions even among opposition factions over whether to negotiate or escalate the unrest.
Bahrain's Shiite majority is seeking a greater political voice in the strategic Sunni-ruled kingdom, which is home to the US Navy's 5th Fleet.
More than 55 people have been killed in the two-year unrest, which began with massive marches on February 14, 2011. Some activists place the death toll higher.
The latest death was a 16-year-old boy killed by police bird shot fire early today in the mainly Shiite village of Dih, west of the capital, Manama, said an activist.
Street battles broke out before dawn in some Shiite neighbourhoods, but opposition groups also have called for a nationwide strike to mark the anniversary.
The main Shiite opposition group Al Wefaq and other factions opened talks with government officials and Sunni envoys last week, but some hardline Shiite groups oppose dialogue amid fears it will not weaken the monarchy's hold on power.
Opposition groups have demanded that the ruling dynasty give up much of its sweeping authority over the country's affairs, including picking all key government and military posts.
Sunni leaders have made some concessions, including handing more oversight power to the elected parliament. But many Shiite protesters say that falls short of their goals.