The U.S. military on Friday admitted that a drone strike it carried out last month in Afghanistan's capital Kabul killed as many as 10 civilians, including seven children, and called the attack a "tragic mistake."

The Aug. 29 strike, which destroyed a vehicle initially believed to have been loaded with explosives, took place in the final stages of the U.S. troop withdrawal from Afghanistan. It was intended to stop an "imminent" threat to the international airport in Kabul, where troops were evacuating civilians.

But Marine Corps Gen. Kenneth McKenzie, head of the U.S. Central Command, told a press conference, "Our investigation now concludes that the strike was a tragic mistake."

According to the latest assessment, it was "unlikely that the vehicle and those who died were associated with ISIS-K or were a direct threat to U.S. forces," he said.

ISIS-K is an affiliate of the Islamic State militant group also known as Islamic State-Khorasan. Just days before, 13 U.S. service members and many Afghans were killed in a suicide bombing near the airport, an attack claimed by the group.

Defense Secretary Lloyd Austin said in a statement, "We apologize, and we will endeavor to learn from this horrible mistake."

The latest announcement cast another shadow over the U.S. troop withdrawal, already marred by chaotic scenes of Afghans desperately seeking to flee the country in the wake of an unexpectedly swift takeover by the Taliban.

It could also raise doubts as to the U.S. military's "over-the-horizon" capabilities, a euphemism for drones, which Washington has said it will rely on for counterterrorism efforts following the troop withdrawal completed in late August.