An Afghan soldier shot and killed a Nato service member in southern Afghanistan, officials said today.
This is the latest incident in a string of similar attacks that has raised concerns about relations between Afghan troops and foreign allies.
International forces and the Afghan army disagreed on exactly what happened.
Lieutenant Colonel Jimmie Cummings, a spokesman for the international military force, said Afghan soldiers detained the gunman after he attacked Nato troops on Tuesday night. The coalition gave no other details.
Afghan National Army commander Sayed Malluk confirmed the shooting, which he said happened during a night patrol in Helmand province's Marjah district. But he said the Afghan soldier, who has been in the army for more than two years, told investigators the shooting was an accident.
It was the sixth report since December 26 of an Afghan soldier - or an insurgent posing as one - turning his weapon on the international troops working to train the Afghan security forces.
The rising number of attacks by supposed friendly Afghan forces has prompted speculation that Taliban insurgents or sympathisers may be infiltrating the national army and police as they rapidly expand to meet a 2014 target for Afghan forces to take over security and most international troops to leave.
Tuesday's attack brought to 34 the number of international troops killed in Afghanistan this year.