Bahrain's police said on Thursday that a man detained over acts of violence and sabotage died of a chronic disease in hospital while in custody, but the opposition said he was tortured to death.
A police official said the man suffered from sickle-cell disease and died of natural causes, state news agency BNA reported.
The main Shi'ite Muslim opposition group, Wefaq, said on its website that the 19-year-old had been injured after being squeezed between two police vehicles as he tried to flee during a protest and that he had been detained and tortured instead of receiving treatment.
Bahrain last year crushed protests led by its Shi'ite Muslim majority demanding an end to sectarian discrimination and limits to the authority of the Sunni ruling family, relying in part on backing from troops from fellow Sunni-led Gulf Arab states.
As violence rises ahead of the anniversary of last year's pro-democracy protests, the Interior Ministry said in a statement that 41 policemen were injured earlier this week, as protesters threw metal rods, rocks, bottles and petrol bombs directly at the riot police.
More than a thousand people were detained in the crackdown last year and at least four died in custody. An inquiry commissioned by Bahrain into the protests and crackdown found systematic abuse of detainees, including torture.
Amnesty International urged Bahrain on Thursday to investigate its use of tear gas against frequent protests in the Gulf state, citing a Bahraini rights group as saying 13 people had died from its indiscriminate use.
The rise in fatalities and eyewitness accounts suggest that tear gas is being used inappropriately by Bahraini security forces, including in people's homes and other confined spaces, said Hassiba Hadj Sahraoui, an Amnesty regional deputy director.
Washington, which bases its Fifth Fleet on the Gulf island, has linked a $53 million arms sale to the kingdom's response to the inquiry. Bahrain has said it is implementing the inquiry's recommendations, but the top U.N. human rights official argues that Bahrain is not punishing those who have committed abuses.
Given the government of Bahrain's malicious misuse of tear gas, the U.S. government should continue its current policy to not issue new licenses for riot control equipment that have the potential for harmful misuse, Hans Hogrefe, chief policy officer of Physicians for Human Rights, said in a statement.
The U.S. should hold fast to its decision to delay a pending $53 million arms sale to Bahrain - a country whose recent actions demonstrate that it cannot be trusted to use these materials within the bounds of the law, he said.
The Interior Ministry said last month it would begin recording the questioning of detainees in line with the recommendations of the inquiry, which also disputed Bahrain's claim that the protests were fomented by predominantly Shi'ite Iran.
(Writing by Joseph Logan and Firouz Sedarat; Editing by Sami Aboudi and Roger Atwood)