Two NATO soldiers were shot dead on Saturday by a man believed to be a member of a controversial Afghan police force in southern Afghanistan, the US-led military said.
The attack means that so far this year, Afghan security personnel have shot dead at least 47 NATO soldiers, the majority of them American, threatening to jeopardise Western plans to train Afghan forces to take over when they leave in 2014.
"An individual believed to be an Afghan Local Police (ALP) member turned his weapon against (NATO's) International Security Assistance Force (ISAF) service members in southern Afghanistan today, killing two," ISAF said.
The attacker was killed in return fire, the military said, refusing to disclose the nationality of the victims.
The police spokesman for southern province Helmand, where British and American troops dominate the NATO contingent, said the incident happened in the provincial capital Lashkar Gah on Saturday afternoon.
The attack came just two weeks after US special forces suspended training for about 1,000 recruits to the ALP.
The force -- which has around 16,000 members -- is US-sponsored and recruited to fight Taliban insurgents in remote areas of the Afghan countryside, though it has been accused of corruption and violence towards civilians.
Training for the mainstream police and the Afghan army -- carried out by NATO rather than the US -- has not been affected.
Afghanistan says it has arrested or sacked hundreds of Afghan soldiers for suspected insurgency links in a bid to stem a trend that threatens to undermine Western plans for a troop withdrawal.
NATO attributes around 75 percent of the attacks to grudges, misunderstandings and cultural differences. The Afghan defence ministry this month published a hastily-written brochure for 195,000 members of the Afghan army with advice on how to behave around and not misunderstand Western soldiers.