Police in Bahrain have claimed self-defence after a youth of 16 was killed during a riot but the opposition say he was kicked on the ground.
The Gulf state's interior ministry said the youth had been among a crowd throwing petrol bombs at police on Friday night, in the Muharraq area.
But the Shia Muslim opposition party al-Wefaq said the boy had been the victim of a "barbaric" attack.
Protests against Bahrain's Sunni Muslim monarchy erupted last year.
The opposition say more than 45 people have been killed in demonstrations since June 2011, when the government lifted martial law.
The latest death came a day after prominent human rights activist Nabeel Rajab was jailed for three years for taking part in "illegal gatherings".
Friday also saw tension in Bahrain as Shia Muslims marked Jerusalem Day in support of Palestinians.
In a statement to Reuters news agency, the government said: "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.
"Despite warning shots by the police the attack continued; so security personnel dealt with the case according to its legal authority."
Police say 700 officers have been injured in riots since martial law was lifted, Reuters reports.
Wefaq said in a statement that Hussam al-Haddad had been "martyred after being brutally attacked".
According to the opposition Bahrain Centre for Human Rights, witnesses saw the security forces firing gunshot pellets at him before men in plainclothes kicked him repeatedly as he lay on the ground while police stood by.
Graphic video was posted online of a pellet-riddled body, said to be that of Hussam al-Haddad, in a hospital room, surrounded by distraught relatives. The video could not be verified independently.
His funeral is said to have passed off peacefully on Saturday.
Shia Muslims, who make up the majority of Bahrain's population, have been pushing for greater rights, arguing that they have been marginalised.
The monarchy denies this and blames unrest on the influence of neighbouring Iran, the region's biggest Shia Muslim state.