A man in an Afghan uniform opened fire on a group of Americans at a base in the south of the country, killing a US soldier and wounding another.
Military spokesman General Mohammad Zahir Azimi said the gunman was also killed in the shootout yesterday. He said an investigation was trying to determine whether the gunman was a member of the Afghan military.
A Nato statement said only that a coalition service member had been killed in the incident, apparently by an Afghan soldier, but provided no further details on the victim's nationality.
Gen Azimi said the shooting occurred inside one of the Afghan National Army's bases in Zabul province, about 250 miles south of Kabul.
Gen Azimi said: “Right now, an investigation is going on to determine whether he really was a soldier or someone using an army uniform. And if he was a soldier, what caused the shooting.”
Similar attacks have raised fears of increased Taliban infiltration of the Afghan police and army as Nato speeds up the training of the security forces. In some cases the attackers were Afghan soldiers who turned on Nato troops. Others involved insurgents dressed in Afghan uniforms.
The shooting brought to 11 the number of Nato soldiers killed this month.
On December 29, an Afghan soldier shot dead two members of France's elite 2nd Foreign Parachute Regiment, a part of the Foreign Legion. A week earlier, an Afghan soldier opened fire on coalition troops inside an outpost in western Herat province, wounding a number of alliance troops.
Nato is encouraging the rapidly expanding Afghan security forces to take more responsibility ahead of the coalition's 2014 pullout target date. Nato's training mission hopes have about 350,000 Afghan troops and police trained and ready by then.