Two U.S. soldiers have been killed by a man wearing an Afghan National Security Forces uniform in southern Afghanistan.
A NATO statement said the attacker opened fire on the soldiers' vehicle inside a military compound in Helmand Province early on August 26.
The shooter and "another individual wearing uniform" were wounded when NATO forces returned fire.
An earlier statement said there were two attackers and both had been killed.
The Pentagon said the two NATO soldiers killed were Americans.
Afghan officials said authorities believe an argument sparked the shooting.
So-called "green-on-blue" attacks -- when Afghan soldiers or police turn their guns on international troops -- have been a major problem during NATO's many years of fighting alongside Afghan forces.
The Helmand attack was the first such incident since April.
The Taliban did not immediately claim responsibility for the attack. Western officials say that most such attacks stem from personal grudges and cultural misunderstandings rather than insurgent plots.
The killings have bred mistrust among local and foreign forces, though fewer incidents have occurred in recent years.
Most NATO combat troops pulled out of Afghanistan last year but a small contingent remains, including roughly 10,000 U.S. soldiers.