The decision to drop the largest non-nuclear bomb ever used in combat was made by the top U.S. commander on the ground, officials told Fox News on Friday, after the so-called "mother of all bombs" was used to obliterate an ISIS target in Afghanistan.

Fox News is told that Gen. John Nicholson made the decision on his own. President Trump’s approval apparently was not needed.

Trump himself declined to say Thursday where the order came from, but stressed that he has given the military complete flexibility.

“We have given [the military] total authorization,” Trump told reporters. “Frankly, that’s why they’ve been so successful lately.”

The Massive Ordnance Air Blast bomb, or MOAB, arrived in Afghanistan in early January, and is designed for its psychological effect as much as the damage it causes – the 21,000-pound bomb has a blast radius of one mile.

WHAT IS THE MOAB?

When the Air Force tested the GBU-43/B in 2003 at the start of the Iraq war, the plume from the explosion reached 10,000 feet into the air. Until Thursday, it was never used in combat.

Afghan officials say 36 ISIS fighters were killed in the strike.

The Department of Defense released footage of the strike on Friday. In the 30-second video, the bomb could be seen dropping before it exploded midair. Smoke quickly rose from the impact zone.

Speaking Friday morning in Kabul, Nicholson defended his decision to order its use, saying this was the right bomb and the right time to use it.

He said the U.S. had persistent surveillance over the area “before, during and after” the operation, and they see no evidence of civilian casualties.

There are under 1,000 ISIS fighters in eastern Afghanistan. Nicholson said hundreds of U.S. airstrikes in the past two years have cut the number down by two-thirds.

Senior Air Force officials told Fox News this is a weapon that is used for strategic messaging – it was described as a tactical decision by the commander in Afghanistan, with no real strategic input from Washington.

“We have incredible leaders in the military, we have an incredible military and we’re very proud of them, and this was another very, very successful mission,” Trump said Thursday.

White House Press Secretary Sean Spicer said earlier at his daily press briefing that the strike was done to deny ISIS "operational space."

When asked if the U.S. would consider using the device in other combat zones, Spicer referred questions to the Pentagon.