Afghan National Army soldiers keep watch at a checkpoint ahead of Eid celebrations, on the outskirts of Jalalabad city in Nangarhar province on July 15. (Noorullah Shirzada/AFP/Getty Images)

A U.S. airstrike in eastern Afghanistan killed at least eight Afghan soldiers at a military outpost Monday in one of the deadliest friendly-fire incidents in years, according to Afghan officials.

The assault unfolded around 7 a.m., striking an Afghan National Army outpost in Logar province, south of the capital, Kabul. The area, in the province’s Baraki Barak district, is thought to be a stronghold of Taliban insurgents, said Halim Fedayee, the provincial governor.

A U.S. Apache helicopter struck the post, he said.

“It seems that the coalition made a mistake in coordinating the air raid,” Fedayee said in a telephone interview.

A U.S military spokesman in Kabul said that the military was looking into the report and that he could not provide details or the circumstances of what happened.

“We are aware of an incident involving U.S. forces in Logar province this morning, 20 July,” said Army Col. Brian Tribus, the spokesman. “This incident is under investigation.”

Logar’s police chief, Mohammad Dawood Ahmadi, said eight soldiers were killed in the attack, although other local media reports put the death toll as high as 14. Five soldiers were also wounded, Ahmadi said.

Monday’s incident was the second friendly-fire attack on Afghan soldiers in Logar province since early last year.

In March 2014, an American air assault killed five Afghan soldiers and wounded seven. And in December, a NATO airstrike killed five civilians and wounded six in Logar, days before the U.S.-led military coalition ended its combat mission.

In recent weeks, the United States has intensified an air-assault campaign in eastern Afghanistan, targeting not only the Taliban but also forces aligned with the Islamic State. In June, the United States carried out 106 airstrikes, more than twice the number in May, according to U.S. military statistics. Even so, there are far fewer airstrikes being carried out now than in previous years, a reflection of the diminished U.S. military presence.

By the end of last year, when most U.S. and international forces withdrew from Afghanistan, there had been 2,363 airstrikes in the previous 12 months. At the end of June this year, the figure was 305.

Although the Obama administration has officially declared America’s longest war over, U.S. forces are permitted to engage in counterterrorism operations and in cases where firepower is essential to protect U.S. forces and the Afghan government.

The Afghan army corps commander for the region, Sharif Yaftali, said the U.S.-led coalition “made a very big mistake,” because the strike was carried out during daytime and the outpost was perched on a hilltop, making it visible for U.S. forces to determine that it was controlled by their allies.

“The Afghanistan flag was waving on our post when we came under attack,” Yaftali said.

But a spokesman for the Afghan Ministry of Defense said U.S. helicopters were flying over a battle zone where Afghan soldiers were fighting the Taliban when the aircraft came under fire, apparently from the militants.

“In a reciprocal act, the helicopters fired back, but unluckily, our post was hit,” said Dawlat Waziri, the spokesman.”We have sent a team to investigate this matter.”

Mohammad Sharif contributed to this report.

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