An Afghan border policeman on Monday turned his weapon on Western troops, fatally shooting six of them. NATO did not disclose the nationalities of the slain soldiers, but a Pentagon official said they were American.
The Western military said it was investigating the attack, which took place during a training exercise in Nangarhar province in eastern Afghanistan. The regional commander of the Afghan border police, Gen. Aminullah Amarkhail, said all the trainers were U.S. troops. Pentagon spokesman Marine Col. David Lapan in Washington confirmed the nationalities.
The assailant was killed as well, NATO said.
The attack, the deadliest of its kind in a year, underscored the perils of the intensive Western effort to quickly train large numbers of Afghan police and soldiers, with the aim of handing over security responsibilities to them. The goal of such a transition taking place by the end of 2014 was endorsed at a North Atlantic Treaty Organization summit in Lisbon this month.
However, Taliban fighters on occasion have infiltrated the ranks of police and army recruits. Attacks on Western troops by Afghan security forces have increased over the last year, either during training exercises or at bases where the two forces live side by side.
There were two such incidents in July alone. In one attack, an Afghan soldier killed two U.S. civilian trainers. In another, an Afghan soldier killed three British Gurkhas. In August, an Afghan policeman killed two Spanish paramilitary troops and their interpreter.
Monday's toll was the heaviest in an attack by a member of the Afghan security forces on Westerners since last November, when an Afghan police officer killed five British soldiers at a checkpoint. Recruitment practices were tightened in the wake of that assault, but the Afghan security forces have been growing rapidly, with police and army now totaling about 260,000.
Attacks are also sometimes carried out by insurgents who manage to procure Afghan police or army uniforms. An Interior Ministry spokesman, Zemari Bashary, said it had been established that Monday's assailant was a member of the police, not someone who had stolen a uniform and slipped into the training exercise.
The six fatalities represented the highest one-day U.S. death toll since Sept. 21, when nine Americans were killed in a helicopter crash. This year has been the most lethal of the 9-year-old war for Americans and the NATO force as a whole; 464 Americans were among the 668 coalition troops killed this year, according to the independent website icasualties.org.