KABUL A joint U.S.-Afghan force called in an airstrike on what turned out to be an Afghan army post after taking fire from there before dawn Saturday, killing four Afghan soldiers and prompting an angry demand for punishment from the country's defense ministry.
Both NATO and Afghan authorities described the clash around a snow-covered outpost in Wardak province southwest of Kabul as a case of mistaken identity. NATO called the attack "unfortunate" and promised a full investigation.
Nevertheless, the deadly strike threatens to strain relations between NATO and the Afghan government at a time when both sides are calling for closer partnership in the fight against the Taliban. The fighting came on the heels of several cases of bloodshed between Afghans and Americans in recent weeks.
NATO and Afghan officials said an Afghan interpreter angry over "job issues" shot and killed two U.S. soldiers Friday before he was gunned down by an American service member in the same district as the airstrike. NATO officials said the two attacks appeared unrelated.
Saturday's fighting erupted about 3 a.m. when a group of U.S. Special Forces and Afghan commandos approached a remote Afghan army outpost that was set up about 18 months ago to guard the main highway between Kabul and Kandahar.
NATO said the Afghan soldiers believed the unit was the Taliban and started shooting.
The joint force returned fire and called in the airstrike, which killed the four Afghan soldiers, NATO and the Afghan Defense Ministry said. Seven Afghan soldiers at the checkpoint were wounded, provincial spokesman Shahidullah Shahid said.
"Besides expressing heartfelt condolences to the families of the martyrs, the Afghan Defense Ministry is condemning this incident," an Afghan statement said. "After the investigation is completed, the Defense Ministry wants to bring those responsible to justice."
Associated Press Television News video of the aftermath showed snow around the fortified compound blackened by the airstrike. American armored vehicles stood guard on the highway, about a half mile (a kilometer) from the hilltop outpost, while a U.S. Black Hawk helicopter roamed the skies overhead.
"I am from this area, and I witnessed the entire incident myself," said local resident Khan Mohammed. "Planes arrived and bombed the Afghan National Army checkpoint. They hit some of the houses around the area with mortars."
NATO said the joint force called in the airstrike only after failing to halt the fighting with return fire. The alliance said a joint Afghan-NATO investigation would "determine the facts and circumstances of this unfortunate incident."
"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 in northwestern Afghanistan during close combat as troops searched for a missing U.S. paratrooper who was later found dead.
Afghanistan's Defense Ministry said at the time that the deaths had been caused by "an air attack by NATO forces" during the fighting.
Last year, the top U.S. and NATO commander, Gen. Stanley McChrystal, curbed the use of airpower to assuage rising public anger over civilian casualties. Commanders still have the option of calling in airstrikes if they come under fire and civilians are not at risk.
Saturday's clash and the string of recent deadly encounters between Americans and Afghans are likely to stoke public anger against foreign forces even though the United Nations reported this month that most civilian casualties were caused by the Taliban.
NATO said its troops opened fire Friday on a taxi as it sped toward a patrol in Ghazni province, killing two civilians and wounding another. U.S. soldiers shot and killed an Afghan imam Thursday when his car approached a convoy on the eastern outskirts of Kabul.
Last week, protesters in Ghazni blocked a major highway for three days, claiming that a NATO and Afghan force killed four civilians in during raid there targeting a Taliban official. NATO insisted the four dead were insurgents.
President Hamid Karzai has urged international forces to do more to protect civilians as part of a plan to build public support and lure Afghans away from the Taliban. Karzai announced a plan in London this week to offer jobs and other incentives to Taliban fighters willing to quit the insurgency and to reach out to the Taliban leadership.
On Saturday, the Taliban denied reports that their representatives met with a senior U.N. official to discuss prospects for peace. A statement sent to news organizations said reports of a meeting between the U.N.'s Afghanistan chief, Kai Eide, and representatives of the militants were "futile and baseless rumors."
Eide has not publicly acknowledged such a meeting but U.S. Secretary of State Hillary Rodham Clinton said the U.N. official wanted to "get his own conclusion about the mindset of some of the Taliban members."
The Taliban statement said the report was part of a U.S.-orchestrated "propaganda campaign" and promised to continue the war.