U.S. forces in Afghanistan have dropped the largest non-nuclear bomb on an Islamic State target in Afghanistan, officials said Thursday.

  • 'Mother of all bombs' contains 11 tons of explosives
  • The target was an ISIS tunnel complex
  • US forces says the use of the bomb was to minimize risk to troops

Adam Stump, a Pentagon spokesman, said it was the first-ever combat use of the bomb, known as the GBU-43, which he said contains 11 tons of explosives.

The bomb was dropped from U.S. aircraft at 7:32 p.m. local time Thursday, U.S. military officials said. The target was an Islamic State tunnel complex in the Achin district of Nangarhar province, which is very close to the border with Pakistan.

Press Secretary Sean Spicer said in a press conference that the tunnels are used by ISIS to easily target U.S. officials and Afghan forces. 

"The United States takes the fight against ISIS very seriously," Spicer said. "In order to defeat the group, we must deny them operations space, which we did. ... The United States took all precautions necessary to prevent civilian casualties and collateral damage as a result of the operation."

The Air Force calls it the Massive Ordinance Air Blast bomb. Based on the acronym, the bomb has been nicknamed the "mother of all bombs."

Army Gen. John W. Nicholson, commander of U.S. forces in Afghanistan, said in a written statement that the strike was designed to minimize the risk to Afghan and U.S. forces conducting clearing operations in the Achin area "while maximizing the destruction" of IS fighters and facilities. He said IS has been using improvised explosive devices, bunkers and tunnels to strengthen its defenses.

"This is the right munition to reduce these obstacles and maintain the momentum of our offensive against ISIS-K," he added, using the U.S. military's acronym for the IS affiliate.

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.

Information from CNN and the Associated Press was used in this report.