A man wearing an Afghan army uniform shot and killed a NATO service member Saturday in southern Afghanistan, the U.S.-led coalition said.
The shooting was part of a spate of weekend attacks that killed at least nine people, including two other foreign troops.
The uniformed gunman escaped after killing the NATO trooper, and it was not known if he was a member of the Afghan army or a militant in disguise. A manhunt, led by members of the Afghan national security forces, was under way, NATO said.
Afghan defence officials could not immediately be reached for immediate comment.
Insurgents have often disguised themselves in the uniforms of Afghan security forces to infiltrate heavily guarded military bases and target international and government forces. Enlisted soldiers and police also have turned on their NATO and Afghan colleagues -- sometimes because arguments have inflamed tensions or because of an alliance or sympathy with the Taliban.
Since March 2009, the coalition has recorded more than 20 incidents where a member of the Afghan security forces or someone wearing a uniform used by them killed coalition forces.
Militants hope to undermine trust between coalition and Afghan forces, who are increasingly partnered to prepare the Afghans to take the lead in securing the nation so foreign troops can withdraw by the end of 2014. Last year, there were 10,400 partnered operations -- up from 530 in 2009, the coalition said.
NATO also reported the killings of two other service members -- one in a roadside bombing Saturday in southern Afghanistan and another in an insurgent attack Friday in the west.
Those deaths raised to 30 the number of international troop deaths in Afghanistan so far this month, including at least 14 Americans, according to an Associated Press tally.
Also in the west, insurgents ambushed an army patrol in the Bala Buluk district of Farah province, killing at least six Afghan soldiers, the Defence Ministry said Saturday.
Ministry spokesman Mohammad Zahir Azimi said 10 other soldiers were wounded in the gunbattle. Azimi said the patrol was part of an Afghan military operation that had killed at least 12 militants.