KIM GAMEL, Associated Press
KABUL - A NATO official says an Afghan interpreter killed two U.S. service members before he was killed himself at a combat outpost in eastern Afghanistan.
The new details emerged Saturday, a day after the deaths were announced in a brief statement.
The official, who spoke on condition of anonymity because he wasn't authorized to release the information, says the attack occurred in Wardak province.
First reports indicated three Americans were killed but the official said one of the dead was an Afghan.
It wasn't immediately clear why the interpreter opened fire.
A clash between U.S. and Afghan troops Saturday that left four Afghan soldiers dead also occurred in Wardak province. But the official says the incidents don't appear to be related.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
KABUL (AP) -- NATO forces clashed with Afghan troops Saturday at a snow-covered highway outpost, calling in an airstrike that killed four Afghan soldiers, U.S. and Afghan officials said.
Afghanistan's Defense Ministry condemned the incident and demanded punishment for those responsible. NATO called it a "regrettable incident and announced an investigation.
The deaths are likely to strain relations between NATO and Afghan forces at a time both are calling for a closer partnership in the fight against the Taliban.
The fighting began about 3 a.m. in the eastern Wardak province, when a joint NATO-Afghan force traded fire with another Afghan unit manning the outpost. NATO troops then called in an airstrike, killing the four Afghans, NATO and the Afghan ministry said.
Neither group confirmed the nationality of the NATO soldiers. Associated Press Television News footage of the aftermath showed American armored vehicles on the highway, about a half mile (a kilometer) from the hilltop outpost. The snow outside the fortified compound was blackened by the airstrike.
"Besides expressing heartfelt condolences to the families of the martyrs, the Afghan Defense Ministry is condemning this incident," the Afghan statement said, adding a delegation had been sent to the area to investigate. "After the investigation is completed, the Defense Ministry wants to bring those responsible to justice."
Provincial officials said the fighting was due to a misunderstanding as the joint NATO-Afghan force returned from an operation in the Sayed Abad district. Provincial spokesman Shahidullah Shahid said seven Afghan soldiers also had been wounded.
NATO said the Afghans began shooting first and the joint force returned fire before calling in the airstrike.
"We work extremely hard to coordinate and synchronize our operations," NATO spokesman Brig Gen. Eric Tremblay said.
It was believed to be the first fatal friendly fire incident since November, when eight Afghans -- four soldiers, three policemen and an interpreter -- were killed during close combat amid a search for a missing U.S. paratrooper.
Afghanistan's Defense Ministry said at the time that the deaths had been caused by "an air attack by NATO forces" during the fighting.
Saturday's incident followed the deaths Friday of two U.S. service members and one U.S. employee who were killed in eastern Afghanistan. In a statement announcing the deaths, NATO did not specify the circumstances or give further details pending an investigation.
That suggested the deaths may not have been due to hostile fire.
Also Saturday, NATO said its troops opened fire on a taxi the day before as it sped toward a patrol, ignoring warning shots. Two civilians were killed and one was wounded in the shooting, which occurred in the Muqor district of Ghazni province.
U.S. soldiers shot and killed an Afghan imam Thursday when his car approached a convoy on the eastern outskirts of Kabul.
Elsewhere, joint NATO-Afghan forces came under attack in the northwestern province of Badghis at about 1 a.m. Saturday (2030 GMT Friday; 3:30 p.m. EDT Friday), prompting a gunbattle and an airstrike that killed eight militants, including a group leader, deputy provincial police chief Abdul Jabar Khan said.
Associated Press writer Rahim Faiez contributed to this report.