The turncoat attack happened at an Afghan army base in southern Uruzgan province and the shooter escaped, said Abdul Hamid Wardak, the Afghan army commander for southern Afghanistan.
NATO confirmed that one of its service members was killed by a man in an Afghan army uniform but did not provide further details. Both NATO and the Afghan government said they are investigating.
Tension has been high between the two forces in recent days. On Saturday, a NATO airstrike inadvertently killed women and children. The international coalition has reduced the number of civilians killed in operations, but Afghan officials say any civilian deaths are unacceptable.
In other violence around Afghanistan, a suicide bomber blew up an explosives-packed car at the gates of an Italian military base Monday in one of two attacks on the relatively secure western city of Herat, killing at least five Afghans in a major commercial center slated to be handed over by NATO to Afghan control in July.
The bombings claimed by the Taliban were the second major attack in three days as insurgents expand their targets outside the southern and eastern theaters that were the focus of American offensives last winter.
The Associated Press contributed to this story