Teenager killed in Bahrain anniversary protests
The Bahraini government has announced an investigation into the death of a teenage boy during protests marking the second anniversary of a failed uprising.
Anti-government demonstrators have set up road blocks and clashed with members of the security forces.
Opposition groups have called for a general strike.
Meanwhile, Amnesty International has called for the release of what it calls Bahrain's "prisoners of conscience".
The call by the human rights organisation comes on the anniversary of a protest movement that has led to two years of unrest and violence.
The organisation has adopted 22 political activists as prisoners of conscience, including several sentenced to life imprisonment.
Amnesty International Middle East and North Africa Deputy Director Hassiba Hadj Sahraoui said: "The government of Bahrain cannot carry on imprisoning people simply because it can't take criticism."
He added: "Many of the allegations put forward by the prisoners of conscience have still not been investigated by the authorities."
The Bahraini government has rejected the criticisms saying there are no political prisoners in the country.
Rioters block roads
Correspondents say that Thursday's protest could mar reconciliation talks which began last week between opposition groups and the government and its loyalists in a bid to end political deadlock.
Witnesses said that the protest turned violent when police fired shotguns and teargas to disperse the crowds, wounding several people.
The website of the main opposition al-Wefaq group said that the boy, 16, was killed on Thursday morning in the village of Daih "when the regime forces targeted him with birdshot at close range".
It says that the the teenager "sustained a serious injury to his stomach" and was taken to hospital before he died.
However the Chief of Public Security Major-General Tariq Hassan al-Hassan issued a statement saying that police had come under attack from rioters "with rocks, steel rods and Molotov cocktails. Warning shots were fired but failed to disperse the advancing crowd who continued their attack. Officers discharged birdshot to defend themselves".
According to the chief, it was at that point "at least one protester was injured" and subsequently died of his wounds at the country's main hospital, the Salmaniya Medical Complex.
The police chief warned people not to use the death "for political purposes or as an excuse to engage in criminal or riotous behaviour".
The interior ministry said rioters had blocked several roads and security forces were seeking to restore order but according to the police chief traffic was flowing freely in most areas of the capital Manama.
Witnesses had earlier reported that roads connecting villages around the capital had been blocked, while schools for Westerners remained closed.
A British expatriate businessman told the BBC that his area was calm but he was "following embassy advice and not going into the city centre".
Last month Amnesty conducted a research trip to Bahrain where it met seven prisoners of conscience detained in Jaw prison in the capital, Manama.
They included Nabeel Rajab, head of the Bahrain Centre for Human Rights, who was given a two-year sentence for encouraging "illegal gatherings".
Mr Rajab, 48, is quoted as telling the Amnesty researchers he was warned by prison authorities not to speak in English or talk about human rights.
The pro-democracy activist is one of the most well-known in the Arab world, with more than 185,000 followers on Twitter. He spearheaded protests which have rocked the kingdom since February 2011.
'No political prisoners'
In a statement to the BBC responding to Amnesty's charges, a Bahraini government spokesperson said: "The Government has reiterated several times that there are no political prisoners currently in Bahrain. The Government supports the right to express oneself freely, as long as the mode of expression does not violate the freedoms of others as stipulated in Article 29 of the UN Declaration of Human Rights. Citizens continue to voice their concerns in in Parliament, as well as exercising the freedom of press, just like in any modern society."
On 14 February 2011, peaceful protesters took over an iconic Bahraini monument, Pearl Roundabout. Three days later security forces cleared the site using tear gas, batons and birdshot.
At least two protesters died and hundreds were injured.
As violence escalated 35 people, including five police officers, were killed, hundreds more were hurt and thousands jailed in February and March 2011.
The vast majority were Shia Muslims in a country ruled by a minority Sunni royal family.
Since then, opposition and human rights activists say another 45 people have been killed, a figure which the government disputes.
Although many people have been released, 13 activists and politicians including the leader of the secular Waad party, Ibrahim Sharif, remain in jail.
They have been convicted and in some cases given life sentences on evidence that is widely accepted to have been obtained under torture.