The protests could mar reconciliation talks that began on Sunday
A Bahraini teenager was killed by security forces on Thursday, an opposition website reported, as activists demonstrated on the second anniversary of an uprising demanding democratic reforms in the US-allied Gulf Arab state.
The protests could mar reconciliation talks that began on Sunday between mostly Shi'ite Muslim opposition groups and the Sunni-dominated government to try to end two years of political deadlock in the island kingdom, which is home to the US Fifth Fleet.
Mass protests that erupted in the island state in February 2011 at the height of the Arab Spring were crushed, but small demonstrations continue on an almost daily basis demanding greater rights for Bahrain's Shi'ite majority and an end to the absolute power of the Sunni ruling family.
The website of the main opposition group Wefaq said a young man identified as Ali Ahmed Ibrahim al-Jazeeri had died in the village of Diya near Manama in an area mostly inhabited by Shi'ites. It said Jazeeri, born in 1996, had been shot by security forces using exploding bullets, banned internationally.
Dozens of people were also hurt in the violence, some by tear gas and other more seriously, it said.
The government's information department said a 16-year old boy had been brought to the Salmaniya Medical Complex in the capital Manama at 7 am (0400 GMT) and had been pronounced dead on arrival.
"The cause of death is as yet unknown. The case has been referred to the public prosecution and a thorough investigation is being conducted," it said in a statement, urging people to remain calm and "not to spread unfounded rumours".
Witnesses said at least three policemen had been injured in clashes that began early in the morning. Many roads connecting villages around Manama were closed, while schools for Westerners remained shut for fear of violence, they said.
The Interior Ministry said rioters had blocked a number of roads, and security forces were seeking to restore order.
An international inquiry commission said in a report in November 2011 that 35 people had died during Bahrain's uprising. The dead were mainly protesters but included five security personnel and seven foreigners. The report said five people had died from torture.
The opposition puts the death toll at more than 80.
Bahrain's opposition and government resumed reconciliation talks on Sunday for the first time since July 2011.
Officials said delegates had agreed at Wednesday's session on some ground rules for the talks, including the role of government representatives and mechanisms for implementing any agreement, paving the way for further sessions next week.
The Shi'ite-dominated opposition wants a constitutional monarchy and a greater say in the running of the country, including an end to what it says are decades of discrimination against Shi'ites, especially in the security forces. The government denies that there is discrimination.