NEW YORK (CBSNewYork) — The United States has dropped the military’s largest non-nuclear bomb on an ISIS cave complex in Afghanistan, a Pentagon spokesman said.

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It happened in the Nangarhar Province on the border with Pakistan.

“We targeted a system of tunnels and caves that ISIS fighters used to move around freely making it easier for them to target U.S. military advisers and Afghan forces in the area,” White House Press Secretary Sean Spicer said. “The United States takes the fight against ISIS very seriously and in order to defeat the group we must deny them operational space.”

Spicer said the U.S. took “all precautions necessary” to prevent civilian casualties and collateral damage.

President Donald Trump called it a “very successful mission” and said he’s “very proud of our military.”

“We have the greatest military in the world, and they’ve done a great job as usual,” he said. “So we have given them total authorization, and that’s what they’ve done, and frankly that’s why they have been so successful lately.”

The Pentagon said the strike has been in the works for a number of months, CBS News reported. Gen. John Nicholson, the commander of U.S. forces in Afghanistan, had to get permission to use the weapon, sources said.

“If you look at what’s happened over the last eight weeks and compare that to what’s happened in the last eight years, you’ll see there’s a tremendous difference,” Trump continued.

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The GBU-43, or Massive Ordnance Air Blast bomb, also known as the “Mother of all Bombs” due to its acronym, contains 11 tons of explosives.

“It hones in on its target. It’s designed to bunker deep inside of its target to make sure it’s destroying not things on the surface but things well under the surface,” former U.S. Army Major Mike Lyons said.

Lyons said the use of the bomb against ISIS means the U.S. means business in the war on terror.

“When you can’t target it with regular conventional methods and you can’t target it with infantry soldiers, you use this kind of weapon system that destroys virtually five square miles without recourse, with considerable collateral damage,” he said.

President Trump was asked if by using the weapon, he was sending a message to North Korean dictator Kim Jong Un.

“I don’t know if this sends a message. It doesn’t make any difference if it does or not,” Trump said. “North Korea is a problem. The problem will be taken care of.”

This is the first time the bomb has been used in combat, Pentagon spokesman Adam Stump said. The weapon was brought into Afghanistan just for this mission, the Pentagon said.

The extend of the damage and whether anyone was killed is not yet clear. The military is conducting an assessment.

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The Pentagon is also reviewing whether to deploy additional trainers to Afghanistan to help bolster U.S. allies there.