Gunman kills two US Army officers in Afghan Interior Ministry Musadeq Sadeq / AP A U.S. military convoy enters the Afghan Interior Ministry in Kabul on Saturday after a gunman killed two American advisers inside. By NBC News' Jim Miklaszewski and wire services ET: A gunman killed two Americans inside the heavily guarded Afghan Interior Ministry in the center of the capital Kabul on Saturday, as protests against the burning of copies of the Muslim holy book roiled the country for a fifth day. The Americans, who were U.S. Army officers, were sitting at their desks inside the government ministry building where they served as advisers to the Afghan security forces when they were shot, NBC News reported. "The assailant is unknown, and an aggressive search is under way to determine who is responsible," Pentagon press secretary George Little said in Washington. Underscoring the severity of the brazen attack, Gen. John Allen, the commander of NATO and U.S. forces in Afghanistan, said all NATO personnel were being recalled from Afghan ministries "for obvious force protection reasons." We are investigating the crime and will pursue all leads to find the person responsible for this attack. The perpetrator of this attack is a coward whose actions will not go unanswered," Allen said in a statement. NATO confirmed that two service members were killed, but spokesman Lt. Col Jimmie Cummings said "initial reports say it was not a Western shooter." He declined to provide further information. The Afghan Taliban claimed that two of their fighters had managed to enter the building in Kabul and kill four "high-ranking U.S. advisers," according to NBC News. U.S. military officials confirmed only two deaths and the Taliban claim could not be independently verified. The Taliban often exaggerate claims of responsibility for terror attacks. Our suicide bomber Abdur Rahman along with another fighter managed to enter the interior ministry and open fire at the Americans. Before carrying out the suicide attack, Abdur Rahman told us on telephone that he had killed four high-ranking Americans. The second fighter successfully escaped the building and has joined his fighters now," the Taliban spokesman, Zabihullah Mujahid, said in a phone call to NBC from an undisclosed location. Military leaders and politicians haven't had much success in stopping the violence, but religious leaders have. He said it was revenge for the desecration of holy Quran by the U.S. forces. Saturday's attack comes as tensions between the Afghans and the Americans are high following the burning of copies of the Muslim holy book at a U.S. base that sparked days of deadly protests. At least 25 people have been killed and hundreds wounded since Tuesday, when it first emerged that Qurans and other religious materials had been thrown into a fire pit used to burn garbage at Bagram Air Field, a large U.S. base north of Kabul. Among those dead were two U.S. soldiers who were killed by one of their Afghan counterparts while a riot raged outside their base. President Barack Obama and other U.S. officials apologized and said the burning of Qurans was a terrible mistake, but the incident has sent thousands to the streets in this deeply religious country. In Kunduz, the capital of Kunduz province in northeast Afghanistan, more than 1,000 protesters demonstrated. At first they were peaceful, but as the protest continued they began throwing stones at government buildings and a U.N. office, said Sarwer Hussaini, a spokesman for the provincial police. He said the police were firing into the air to try to disperse the crowd. The U.N. confirmed in a statement that its Kunduz compound was attacked, but said all its staff in Kunduz and in the country were unhurt and accounted for. The statement thanked Afghan security forces for their quick response to the assault. NBC News, The Associated Press and Reuters also contributed to this report.