A 16-year-old boy has been hit by a car and killed after running onto a busy road while being chased by security forces, opposition and human rights activists said.
The interior ministry said the boy, who the opposition named as Ali Radhi, was killed in a "traffic accident" on a highway not far from the village of Diraz, west of Manama.
Maryam al-Khawaja, acting head of the Bahrain Centre for Human Rights, said on her Twitter account: "Confirmed from several eyewitnesses: Ali Radhi was chased by riot police... he went onto the highway to run away, was hit by a civilian car. We hold the Ministry of Interior responsible for his death."
Al Wefaq, the main opposition group, had called on protesters to join weekly prayers on Friday.
Witnesses said security forces fired teargas and blocked roads to stop thousands from joining the prayers.
The group said Radhi was killed as he headed to Diraz to attend prayers led by Shia spiritual leader Sheikh Issa Qassim, answering the call by Al Wefaq, the organisation said on its Twitter page.
Al Wefaq posted pictures on Facebook and Twitter showing worshippers trying to reach Diraz as police allegedly blocked roads to the village, preventing media and non-residents from entering the Shia village.
Elderly people can be seen in the pictures collapsed on the ground after allegedly being hit by tear gas.
Bahraini authorities were not immediately available to comment on Friday, but the call for mass prayers appeared to flout a ban on rallies and protests announced by the interior ministry last month.
Footage posted on YouTube that could not be independently verified showed a teargas canister going off inside a car carrying women who activists said were on their way to the prayers.
One woman was seen collapsing on the ground after exiting the vehicle.
Last year's protests were initially crushed by the kingdom's Sunni Muslim monarchy, with martial law and help from Gulf neighbours. But smaller demonstrations have since resumed and anti-government protesters clash with security forces several times a week.
The violence has intensified in recent weeks. On Monday, the government said five home-made bombs killed two people in Manama.
Bahrain's government said on Wednesday it had revoked the nationality of 31 men for damaging national security, including leading dissidents, parliamentarians, clerics and human rights lawyers.