WATCH: Pentagon holds news briefing as U.S. considers response to killing of 3 soldiers in Jordan

WASHINGTON (AP) — U.S. forces may have mistaken an enemy drone for an American one and let it pass unchallenged into a desert base in Jordan where it killed three U.S. troops and wounded dozens more, officials said Monday.

Watch the briefing in the player above.

Details of the Sunday attack emerged as President Joe Biden faced a difficult balancing act, blaming Iran and looking to strike back in a forceful way without causing any further escalation of the Gaza conflict.

As the enemy drone was flying in at a low altitude, a U.S. drone was returning to the small installation known as Tower 22, according to a preliminary report cited by two 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. One of the trailers where troops sleep sustained the brunt of the strike, while surrounding trailers got limited damage from the blast and flying debris.

WATCH: White House holds briefing as Biden promises action after 3 U.S. troops killed in Jordan

Aside from the soldiers killed, the Pentagon said more than 40 troops were wounded in the attack, most with cuts, bruises, brain injuries and similar wounds. Eight were medically evacuated, including three who were going to Landstuhl Regional Medical Center in Germany. The other five, who suffered minor brain injuries, were expected to return to duty.

The preliminary conclusion was first reported by The Wall Street Journal.

Asked if the failure to shoot down the enemy drone was “human error,” Pentagon spokeswoman Sabrina Singh responded that the U.S. Central Command was still assessing the matter.

The Pentagon identified those killed in the attack as Sgt. William Jerome Rivers, 46, of Carrollton, Ga.; Spc. Kennedy Ladon Sanders, 24, of Waycross, Ga., and Spc. Breonna Alexsondria Moffett, 23, of Savannah, Ga.

The three U.S. Army Reserve soldiers were assigned to the 718th Engineer Company, 926th Engineer Battalion, 926th Engineer Brigade in Fort Moore, Georgia.