WASHINGTON — U.S. forces in Afghanistan on Thursday struck an Islamic State tunnel complex in eastern Afghanistan with “the mother of all bombs,” the largest non-nuclear weapon ever used in combat by the U.S. military, Pentagon officials said.

The bomb, known officially as a GBU-43B, or massive ordnance air blast weapon, unleashes 11 tons of explosives. When it was developed in the early 2000s, the Pentagon did a formal review of legal justification for its combat use.

The Pentagon said it had no early estimate of deaths or damage caused by its attack, which President Donald Trump called a “very, very successful mission.”

The U.S. military headquarters in Kabul said in a statement that the bomb was dropped at 7:32 p.m. local time Thursday on a tunnel complex in Achin district of Nangarhar province, where the Afghan affiliate of the Islamic State group has been operating. The target was close to the Pakistani border.

The U.S. estimates 600 to 800 IS fighters are present in Afghanistan, mostly in Nangarhar. The U.S. has concentrated heavily on combatting them while also supporting Afghan forces battling the Taliban. Just last week a U.S. Army Special Forces soldier, Staff Sgt. Mark R. De Alencar, 37, of Edgewood, Maryland, was killed in action in Nangarhar.