A suicide bomber killed at least two Afghan civilians and wounded four others outside the gates of the U.S. military base at Bagram, just north of Kabul Monday.

The Taliban claimed responsibility for the bombing, saying it was revenge for the burning of Qurans at the facility several weeks ago.

The apparently unintentional burning of the Muslim holy books has sparked violent anti-American protests across Afghanistan. Thirty people have been killed and U.S.- Afghan relations have been frayed.

U.S. President Barak Obama apologized to Afghan President Hamid Karzai — a gesture that angered many conservative politicians and commentators in the United States.

But the commander of NATO troops in Afghanistan, American General John Allen, tells ABC television that the apology was the right thing to do and said it likely saved lives. General Allen says an investigation into the Quran burning is under way.

The books were were sent to an incinerater along with non-holy books after U.S. military officers suspected detainees in a jail next to Bagram were communicating with each other by putting notes inside books taken from the jail's library.

U.S. soldiers were reportedly unaware that Qurans were among the books being burned. Four of the Qurans were badly burned before Afghan workers could put out the flames.

The New York Times newspaper has quoted a U.S. official close to the joint Afghan-American investigation into the incident as saying at least six people involved in the burning, including American military leaders and an American interpreter, could face disciplinary action.