A spokesman for the NATO-led International Security Assistance Force in Afghanistan said a man wearing the uniform of the Afghan National Army shot and killed a soldier from the international coalition in southern Afghanistan.
The spokesman said the attacker was killed when coalition forces returned fire.
An Afghan Army commander said the attack in the Shah Wali Kot district of Kandahar Province was carried out by an officer in Afghanistan's special forces.
In Washington, a Pentagon spokesman said the slain coalition soldier was from the United States.
The incident happened on April 25.
The coalition said it is investigating the attack.
There have been several similar attacks recently by infiltrators from the Taliban or Afghan soldiers angered by the massacre of 16 Afghan civilians by a suspected U.S. soldier and the accidental burning of Korans at Bagram Airfield north of Kabul.
Based on reporting by AP and AFP