DUBAI: A 16-year-old protester was killed after what opposition activists in Bahrain said was a "brutal attack" by security forces, but which the Bahrain government described as a defensive response to a petrol bomb attack on police.

The opposition says more than 45 people have been killed in protests since June 2011, when the government lifted martial law it had imposed to help quash pro-democracy demonstrations by its Shi'ite Muslim majority inspired by revolts against repressive dynasties across the Arab world.

However, the Interior Ministry says protesters have injured more than 700 police officers in clashes and that the police, who do not use live fire, have been exercising restraint.

The protester's death - after a demonstration on Friday night - came as the United States, an ally of Manama, expressed concern over Bahrain's jailing of a prominent opposition
activist, Nabeel Rajab, for three years.

The government identified the dead youth as 16-year-old Hussam al-Haddad, and said he had been among protesters throwing petrol bombs at police and had died after being taken to
hospital.

The opposition Bahrain Centre for Human Rights said witnesses had seen the security forces fire birdshot at Haddad before men in plainclothes kicked him repeatedly as he lay on
the ground while police stood by.

The main opposition Wefaq movement said in a statement in Arabic that Haddad had been "martyred after being brutally attacked" and activists posted what they said were pictures of
his body, apparently severely bruised and marked by dozens of birdshot wounds.

Reuters was unable to verify the pictures independently.

The government said police were acting in self defence.

"Terrorists launched petrol bombs at close range, forcing the police to take the necessary actions to defend themselves and innocent bystanders from the potentially lethal attack," the
Information Affairs Authority said in an emailed statement in English.

"Despite warning shots by the police the attack continued; so security personnel dealt with the case according to its legal authority," it added, citing the police chief of the Muharraq
district where the incident took place.

Hundreds of people marched peacefully through the Muharraq district for Haddad's funeral on Saturday, witnesses said. 

Rights groups have accused the government of firing teargas canisters at close range and into confined spaces as a weapon instead of using the gas solely to disperse protests, something the government has denied.

Bahrain's own inquiry into the overall uprising and subsequent violence said at least five people had died under torture in government custody and recommended quashing verdicts
issued against protesters by a military court.

On Wednesday, the country's top appeals court reduced sentences handed down to 11 people accused of attacking a soldier during the turmoil.

Bahrain's Shi'ites say they have been marginalised in the tiny island kingdom's political and economic life, but the Sunni-led government denies this. 

The ruling family has rejected the main opposition demand  for an elected parliament with full powers to pass laws and form governments, but has enacted reforms to increase parliamentary scrutiny over ministers and has said it will reform the police. 

On Tuesday, King Hamad bin Isa Al Khalifa said the country's problems were caused by "foreign plots", restating the government's accusation that the uprising was instigated by
Shi'ite Iran, something that both Tehran and protesters deny.

However, he added that the government was "sparing no effort to solve" its internal problems and that Bahrain had become a country of democracy and human rights. 

Wefaq said the speech showed Bahrain's government was not coming under pressure from Washington to hold talks with the opposition.

The U.S. Fifth Fleet is based in Bahrain, on the west of the Gulf, a transshipment route for 40 percent of the world's seaborne oil exports which is bordered to the north by Iran.

On Friday, the U.S. State Department said it was "deeply concerned" by the jailing of Rajab, a prominent opposition leader, on charges of leading illegal gatherings. 

"We have repeatedly urged the government of Bahrain to take steps to build confidence across Bahraini society, and to begin a meaningful dialogue with the political opposition and civil
society. Excessive punishment for peaceful expression ... will not contribute to those efforts," it said in a statement.

Bahraini Information Minister Samira Rajab said on Saturday that the activist had been tried fairly and had enjoyed full access to legal aid. AGENCIES