A United States soldier murdered 16 Afghan citizens Sunday, Afghan officials have reported. The soldier left his base alone and went from house to house shooting.

Nine children were among the dead, said President Hamid Karzai, who termed the killings “unforgiveable.”

NATO officials confirmed that a soldier had fired on civilians, but could not confirm the number of victims. Officials condemned the attacks, and said victims were being given treatment in NATO facilities.

The soldier involved will be “held fully accountable,” said General John Allen.

Tensions in Afghanistan have been particularly high recently due to an incident in which NATO troops accidentally sent copies of the Koran to be burnt as garbage. The books had been confiscated from Taliban prisoners who had been using them to send messages.

Locals responded to the near-burning of the Koran with massive riots. A Taliban terrorist attacked a NATO base in revenge, killing nine people.