WASHINGTON (AP) — The Pentagon retreated from its defense of a drone strike that killed multiple civilians in Afghanistan last month, announcing Friday that an internal review revealed that only civilians were killed in the attack, not an Islamic State extremist as first believed.

“The strike was a tragic mistake,” Marine Gen. Frank McKenzie, head of U.S. Central Command, told a Pentagon news conference.

For days after the Aug. 29 strike, Pentagon officials asserted that it had been conducted correctly, despite numerous civilians being killed, including children. News organizations later raised doubts about that version of events, reporting that the driver of the targeted vehicle was a longtime employee at an American humanitarian organization and citing an absence of evidence to support the Pentagon’s assertion that the vehicle contained explosives.

McKenzie said the vehicle was struck “in the earnest belief” that the targeted vehicle posed an imminent threat.

“I am now convinced that as many as 10 civilians, including up to seven children, were tragically killed in that strike,” McKenzie said. “Moreover, we now assess that it is unlikely that the vehicle and those who died were associated with ISIS-K, or a direct threat to U.S. forces,” he added, referring to the Islamic State group’s Afghanistan affiliate.

This is a developing story.