Afghanistan's Defense Ministry demands that those responsible be punished. In an unrelated incident, NATO reports that an Afghan interpreter shot dead two U.S. troops a day earlier.
Reporting from Kabul, Afghanistan - Western forces killed four Afghan troops Saturday in an airstrike, and military officials disclosed that an Afghan interpreter had shot dead two U.S. service members a day earlier, in a rare concentration of deaths at the hands of allies.
Even more unusually, the lethal incidents occurred in the same district of Wardak province, west of the capital, Kabul, but officials said they did not appear to be related.
The deaths came on the heels of a conference in London at which nations contributing troops and aid worked to lay the groundwork for an eventual Western withdrawal.
Central to that scenario is the close cooperation of Afghan security forces and foreign mentors as Afghans prepare to assume responsibility some years from now for safeguarding the country.
But relations between the two sides are sometimes marked by mistrust.
The NATO airstrike on an Afghan army outpost marked the second friendly fire incident in less than three months that has killed several Afghan troops. Accounts by both sides suggested that in predawn darkness and amid rugged territory, Western and Afghan troops mistook each other for insurgents, setting off a clash.
NATO expressed regret over the incident, but in a reflection of continuing tensions between Western forces and the Afghan government, the Defense Ministry issued a harshly worded statement demanding that those responsible be punished.
More than 24 hours after the deaths of two U.S. service members at the hands of an Afghan interpreter, the details remained unclear. An American military official, speaking on condition of anonymity, said the confrontation appeared to have been triggered by a personal dispute rather than insurgent loyalties on the interpreter's part.
The interpreter was shot and killed by another U.S. soldier.
The two incidents come at a time of growing friction over the misplaced use of force. On Friday, Western troops shot and killed two Afghan civilians as their taxi approached a patrol in Ghazni province. A day earlier, U.S. troops killed an imam, or mosque prayer leader, as he was driving near their convoy in Kabul.
Karzai has long been an outspoken critic of civilian casualties caused by foreign troops, urging that they take more care to prevent accidental deaths. A recent U.N. report says the proportion of civilian deaths caused by coalition and Afghan troops fell in 2009 under strict new rules of engagement.
Saturday's airstrike was under joint investigation by Afghan and Western officials, both sides said. In addition to the four deaths, at least seven Afghan troops were injured.
Military officials did not disclose the nationalities of the Western troops involved, but most of the foreign forces in that area are American, and U.S. military vehicles were seen in the vicinity.
NATO said the clash began when a joint Western-Afghan patrol came under fire as it was returning from a nighttime operation about 3 a.m. in the Sayedabad district.
Western military officials suggested that Afghan soldiers manning a nearby outpost might have mistaken the patrol for insurgents and fired the initial shots. After a firefight broke out, the allied forces called in the airstrike, apparently not realizing that the source of fire was an Afghan army position.
"We work extremely hard to coordinate and synchronize our operations," said Brig. Gen. Eric Tremblay, a NATO spokesman. "This is a regrettable incident, and our thoughts go out to the families of those killed and wounded."
Early in November, seven Afghan security forces and an interpreter were killed in apparent fire by NATO troops in Badghis province in the midst of a search-and-rescue mission.