Second day of protests rocks Bahrain
The BBC's security correspondent Frank Gardner says the day has been "highly charged"
A second day of clashes has rocked the Gulf kingdom of Bahrain after two people were killed on Thursday.
A police officer and a 16-year-old protester died in Thursday's protests to mark the second anniversary of demonstrations against the rule of the country's Sunni royal family.
Friday saw police using tear gas and stun grenades to disburse several thousand anti-government marchers.
Protesters blocked the Boudaya highway - a major road into the capital Manama.
With unrest continuing late into the evening, the US ambassador to Bahrain has called for calm.
Violence condemned
Thousands or protesters blocked the Boudaya highway - a major road into the capital Manama
The rally had been called by opposition political societies calling for a constitutional monarchy, but many in the crowd were shouting for the end of the monarchy and the ousting of the royal al-Khalifa family.
One eyewitness told the BBC that police had fired on the marchers without any apparent provocation, adding that people had run into a commercial mall to escape the police.
US Ambassador Thomas Krajewski expressed "deep concern" about the increase in violence.
"We strongly condemn all violent and destructive activity, including attacks on police and violence against demonstrators," he said.
Analysis
Peaceful activists are growing increasingly concerned that militant young Bahrainis are hijacking the protest movement. One activist told the BBC: "We want peaceful demonstrations where women, children and older people can make a protest and be safe. The violence is hijacking what we are trying to do."
But masked Shia youth armed with petrol bombs and projectiles are launching more and more attacks on the police. One observer who asked not to be named described them as "very aggressive and fanatical". When asked what they want, the observer said, the radical young protesters say they want to "kick out the regime and bring in a republic".
The increasing radicalisation is creating a major dilemma for al-Wefaq, the main opposition society. The government accuses it of not doing enough to curb the violence. Al-Wefaq, together with other opposition societies has, issued statements condemning violence.
Police chief Tariq Hassan al-Hassan said that the police officer, Mohammed Asif, died after being struck by a projectile.
"While Asif and several other police officers were securing roads a group of rioters attacked with Molotov cocktails, steel rods and stones."
He called it an "unprovoked attack".
The protests and violence come as the government and opposition start a national dialogue aimed at easing the country's crisis. The majority Shia community in Bahrain is pressing for greater political rights.
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.
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