A suicide bomber killed at least two civilians on Monday after detonating explosives at the gates of the NATO base where copies of the Koran were burned, Afghan officials said.

The bomber targeted a vehicle belonging to the NATO-led International Security Assistance Force (ISAF), said district governor Kabir Ahmad Rahil, adding there could be foreign casualties, although a NATO spokeswoman said no coalition troops had been harmed in the attack on Bagram airfield.

Four more civilians were wounded in the attack, Rahil said.

The Taliban claimed responsibility for the attack, saying it was revenge for the Koran burning, spokesman Zabihullah Mujahid said in a text message to media. He added that a number of Americans were killed and their tanks destroyed in the attack, although the Islamist group often exaggerate casualties.

Afghanistan's army chief has said the burning of Korans last month at the NATO base an hour north of Kabul advanced the Taliban's cause and warned that any repeat of such negligence by Western forces could be disastrous.

The United States described the burnings as unintentional and apologised, but this failed to quell the widespread protests that killed at least 30, wounded hundreds and plunged Afghan-American relations to a new low.

The Koran burnings could also be behind the deaths of up to six American soldiers, including two high-ranking officers in the interior ministry, believed to be shot by Afghan security forces.

(Reporting by Mirwais Harooni and Amie Ferris-Rotman; Editing by Ed Lane)