A gunman in Afghanistan has killed two American military officers in NATO's International Security Assistance Force.

Reports from Kabul say the victims are a U.S. colonel and a major, both shot to death in a highly secure command center at the Afghan Interior Ministry.

Many Americans on the NATO force work within Afghan ministries as advisors.

NATO said in a statement Saturday that an individual “turned his weapon against” the service members, but did not provide details on who the shooter or the victims were.

Violence continued across Afghanistan Saturday, in the the fifth straight day of protests over the burning of Qurans.

Hundreds of rock-throwing protesters attacked a United Nations compound in northern Afghanistan. Officials say at least three people died and 47 were injured in the melee in Kunduz.

Authorities say at least 27 people have died since Tuesday after reports surfaced that NATO troops had burned copies of the Quran at Bagram Air Base near Kabul.

U.S. President Barack Obama and other U.S. officials have apologized for the desecration of the Muslim holy book, but the apologies have done little to quash the outrage in Afghanistan and neighboring Pakistan.

Meanwhile, Afghanistan's defense ministry says six Afghan soldiers were killed and 16 were wounded Saturday while trying to defuse a roadside bomb.

The ministry says the incident happened in the Muqur district of western Badghis province.