KABUL, Afghanistan – Defense Secretary Leon Panetta is condemning what he calls the murder of two American military officers in Afghanistan's capital.
Pentagon press secretary George Little says in a written statement that Panetta believes Saturday's killings in Kabul are unacceptable.
The nationality of the gunman hasn't been confirmed. The Taliban claimed responsibility for the attack inside a heavily guarded government building, saying it was retaliation for the burning of Korans on a U.S. military base in Afghanistan.
Little says Panetta received a telephone call from his Afghan counterpart, who offered his condolences and apologized for the incident.
Little says Panetta urged the Afghan government to take "decisive action" to protect coalition forces and to curtail violence after a week of unrest sparked by outrage over the burning of the Muslim holy books.
Meanwhile, the commander of NATO and U.S. forces says that all NATO personnel are being recalled from Afghan ministries following an attack at the Interior Ministry in Kabul.
Gen. John Allen says staff are being recalled "for obvious force protection reasons." He says NATO is investigating Saturday's shooting and will pursue all leads to find the person responsible for the attack.
Two U.S. military advisers were killed Saturday at the Afghanistan Interior Ministry in Kabul, though accounts of what led to the clash were unclear.
Contradictory accounts emerged out of Kabul following the shooting.
The Taliban claimed responsibility for the attack, saying it was retaliation for the Koran burnings.
U.S. officials said the assailant remained at large and a manhunt was under way.
The two advisers were shot in the back of the head, according to two Western officials, who spoke on condition of anonymity because they were not authorized to disclose the information.
Initially, reports from the country indicated that the shooting was a result of an altercation between Westerners. But a report by the Wall Street Journal, citing one Western official in Kabul, said the two high-ranking advisers were killed by an Afghan police officer who was upset about the burning of Korans earlier this week at a U.S. military base.
The Associated Press then quoted a NATO official saying the shooter was not a Westerner.
A U.S. official in Washington confirmed that the two killed were American and that they were killed by "an assailant," without giving further information about the attacker. The official spoke anonymously to discuss information that had not been publicly released.
NATO forces have advisers embedded in many Afghan ministries, both as trainers and to help manage the transition to Afghan control and foreign forces prepare to withdraw by the end of 2014. The Afghan Interior Ministry oversees all of the country's police, so has numerous NATO advisers.
The International Security Assistance Force released a statement Saturday condemning that attacks. "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," Gen. John R. Allen said in the statement. "For obvious force protection reasons, I have also taken immediate measures to recall all other ISAF personnel working in ministries in and around Kabul."
At least 28 people have been killed and hundreds wounded since Tuesday, when it first emerged that Korans 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.
President Obama and other U.S. officials apologized and said it 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.
U.N. officials could not be reached for immediate comment.
Tensions between the Afghans and the Americans already were high following the Koran burnings. Anti-American sentiment has been on the rise in the war-weary country, and several foreign troops have been killed by Afghan soldiers in recent months. Some of those shootings have been blamed on personal hostilities, while others have been attributed to Taliban infiltrators.
In a statement, Taliban spokesman Zabiullah Mujahid said the gunman was an insurgent named Abdul Rahman. He said an accomplice inside the ministry helped him get inside the compound. He said the killings were a planned response to the Koran burnings.
"After the attack, Rahman informed us by telephone that he was able to kill four high-ranking American advisers," Mujahid said. The Taliban frequently exaggerate casualty claims.
The Associated Press contributed to this report.