An enemy drone that killed three American troops and wounded dozens of others in Jordan may have been confused with an American drone returning to the U.S. installation, two U.S. officials said Monday.

As the enemy drone was flying in at a low altitude, a U.S. drone was returning to the small desert installation known as Tower 22 and may have been let pass by mistake, according to a preliminary report cited by the officials, who were not authorized to comment and insisted on anonymity,

As a result, there was no effort to shoot down the enemy drone that hit the outpost early Sunday morning. The U.S. troops at the outpost use trailers for their sleeping quarters.

Officials said that of the 34 wounded troops, most had cuts, bruises, traumatic brain injuries and similar wounds. Eight were medically evacuated and the most seriously hurt service member is in critical but stable condition.