By ROBERT BURNS
AP National Security Writer
WASHINGTON (AP) — The Pentagon has retreated from its defense of a drone strike that killed multiple civilians in Afghanistan last month. It announced Friday that a review revealed that only civilians were killed in the attack, not an Islamic State extremist as first believed. Marine Gen. Frank McKenzie, head of U.S. Central Command, called it a “tragic mistake.” For days after the Aug. 29 strike, Pentagon officials asserted that it had been conducted correctly. News organizations later raised doubts, 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.