NATO has recalled all staff working at Afghan government ministries after two U.S. officers were shot dead at close range inside a secure command center at the Interior Ministry in Kabul.

NATO said the decision to order the recall came “for obvious force protection reasons.” It said the official account indicated a member of the Afghan security forces turned his weapon on the Americans who worked as advisers at the ministry.

The Afghan Taliban claimed responsibility for the shooting, and said the attack was retaliation for the burning of Qurans by NATO personnel a week ago. The incident has inflamed passions throughout the country and led to rioting in which dozens of people have died.

The Pentagon described as “unacceptable” the killing of the two officers. A spokesman for U.S. Defense Secretary Leon Panetta said his Afghan counterpart, Defense Minister Abdul Rahim Wardak, had called to apologize for the incident.

Later Saturday, U.S. President Barack Obama called his top commander in Afghanistan, General John Allen, to discuss the ongoing violence in the country, as well as the killing of the two Americans. Mr. Obama expressed his condolences to General Allen and to the families of the victims. He also welcomed a statement by Afghan President Hamid Karzai calling for “dialogue and calm.”

A NATO spokesman, Brigadier General Carsten Jacobson, said a gunman “turned his weapon against” the Americans. There was no word on the fate of the gunman or whether anyone else was involved in the shooting.

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

Hundreds of rock-throwing demonstrators attacked a United Nations compound in northern Kunduz province. Local officials said at least three people were killed and 47 were wounded in the rioting.

Since Tuesday, when reports first surfaced about the Quran-burning incident at Bagram Air Base near Kabul, at least 27 people have died in violent circumstances, including at least two other NATO service members whose killing was claimed by the Taliban.

President Obama and other U.S. officials have apologized for any desecration of the Muslim holy book, but that has done little to quiet the outrage in Afghanistan and neighboring Pakistan.

NATO is conducting a full investigation of the incident, but has not issued a detailed statement yet. Media reports quoted unnamed Western officials as saying it appeared that the copies of the Quran in question and other Islamic readings in the library at Bagram were being used to fuel extremism, and that detainees were writing on the documents to exchange extremist messages.

In a separate incident in western Badghis province, Afghanistan's Defense Ministry said six Afghan soldiers died and 16 were wounded Saturday while trying to defuse a roadside bomb.

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(SOUNDBITE) (English) ISAF SPOKESMAN, BRIGADIER GENERAL CARSTEN JACOBSON, SAYING:

“We are not linking this incident as yet we have to look into the details of what is going to come out over the coming hours. Of course we have had a tense week behind us and it is very regretful to see the loss of life again on this day, and that includes the loss of life that we have seen around demonstrations today and we feel deep sorrow for those who have perished in demonstrations today but also of course this is a very, very tragic incident and we have to look into further details.''

(SOUNDBITE) (English) ISAF SPOKESMAN, BRIGADIER GENERAL CARSTEN JACOBSON, SAYING:

“We cannot confirm any further details about the incident as we are in the early stage of the investigation. With the relevant Afghan authorities, we have to look at all the sides, all the details and we cannot confirm where the killer came from, what his nationality was, whether he was in uniform or not, all these questions are not known and we have to wait for further details.”

AP feed: (Pashto) Attaullah Neyazi, Laghman Provincial Health Director:

“We have received 20 wounded victims and from them two are in critical condition, and those two have been sent to Jalalabad hospital after they were given first aid treatment. Fortunately so far we don't have any cases of deaths reported to us.”

(Pashto) General Abdul Rahman Sarjang, Laghman provincial police chief:

“In the shooting from them (the protesters), two of the intelligence service members were wounded. One police officer was wounded and tens of police, Afghan national army soldiers and intelligence service members were wounded by stones thrown by them (the demonstrators).”