WASHINGTON — The U.S. commander in Afghanistan who ordered use of the "mother of all bombs" to attack an ISIS stronghold near the Pakistani border didn't need and didn't request President Donald Trump's approval, Pentagon officials said Friday.

The officials said that even before Trump took office in January, Gen. John Nicholson had standing authority to use the bomb, which is officially called the Massive Ordnance Air Blast bomb, or MOAB, the largest non-nuclear bomb ever dropped in combat. The bomb, dropped by a special operations MC-130 aircraft, had been in Afghanistan since January.

The officials weren't authorized to speak publicly on the matter and requested anonymity.

The bomb's use has attracted enormous attention, but its aim in Thursday's attack was relatively mundane by military standards: destroy a tunnel and cave complex used by ISIS fighters in a remote mountainous area of eastern Afghanistan.

Initially, Afghan officials said 36 ISIS fighters were killed, but a provincial spokesman in Nangarhar said Saturday that at least four commanders and 94 ISIS fighters were killed. NBC News has not independently verified that death toll.

Afghan officials have said no civilians were killed.

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Gen. Nicholson had a secondary goal in mind with the bombing, however, according to an official who spoke on condition of anonymity in order to discuss internal matters. The official said Nicholson wanted to demonstrate to leaders of the ISIS affiliate in Afghanistan the seriousness of his determination to eliminate the group as a military threat.

Related: Why America Dropped ‘Mother of All Bombs’ on ISIS in Afghanistan

The official said use of the weapon had nothing to do with sending a message to any other country, including North Korea.

The Air Force estimates each MOAB costs about $170,000 to build. It hasn't said how much it cost to develop the bomb or how many exist. An Air Force spokeswoman, Erika A. Yepsen, said the bomb was made "in-house," with some parts manufactured by the Air Force itself, so the overall cost is only an estimate. Most weapons are made by defense companies under written government contracts.

Nine years ago the Air Force published an account of how it came to manufacture the Massive Ordnance Air Blast bomb, known technically as the GBU-43B, a designation that reflects the fact that it is precision-guided. The weapon from which it evolved, the BLU-82 (Bomb Live Unit-82), was about half MOAB's size and was an unguided, or dumb, bomb.

The MOAB was developed and built at Eglin Air Force Base in Florida by the Air Force Research Laboratory Munitions Directorate.

The Air Force account, written in March 2008, said MOAB "started out simply as an idea" that became a request in late November 2002 as the administration of George W. Bush was contemplating invading Iraq to topple President Saddam Hussein.

The Air Force conducted and released video footage of the bomb's final test detonation on March 11, 2003, just days before the U.S. launched its invasion, which successfully removed Saddam from power but led to an unanticipated Sunni Arab insurgency that created a military quagmire and has yet to return Iraq to normalcy.

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Asked about the test on the day it was conducted, then-Defense Secretary Donald H. Rumsfeld said, "There is a psychological component to all aspects of warfare. The goal is to not have a war. The goal is to have the pressure be so great that Saddam Hussein cooperates. Short of that, an unwillingness to cooperate, the goal is to have the capabilities of the coalition so clear and so obvious that there is an enormous disincentive for the Iraqi military to fight against the coalition, and there's an enormous incentive for Saddam Hussein to leave and spare the world a conflict."

The 2008 Air Force account quoted one of the MOAB project leaders, Robert Hammack, as saying many of the bomb parts were engineered and made in-house, and that the project drew so much interest that experts came out of retirement to work on it. Once built, the bomb was transported to an ammunition depot in Oklahoma to be filled with explosive materials and painted.

"A little known fact is why the MOAB is green," Hammack was quoted as saying. "Since we were in such a rush to get the weapon into our inventory to send over to aid the (Iraq) war effort, resources were limited. The weekend the MOAB arrived, the only color available in the amount we needed was John Deere green."