US Forces Afghanistan said the bomb was dropped at 7.32pm Thursday (3.02am Friday NZ time).
"As (ISIS-Khorasan's) losses have mounted, they are using IEDs, bunkers and tunnels to thicken their defence," said General John Nicholson, who heads US Forces Afghanistan.
"This is the right munition to reduce these obstacles and maintain the momentum of our offensive against ISIS-K."
The air force calls the GBU-43, which contains 11 tonnes of explosives, the Massive Ordnance Air Blast bomb. Based on the acronym, it has been nicknamed the "Mother Of All Bombs."
The bomb was delivered via an MC-130 transport plane, according to the Pentagon.
"The GBU-43/B is the largest non-nuclear bomb ever deployed in combat," air force spokesman Colonel Pat Ryder said.
'Message for North Korea'
A former US intelligence officer says the "mother of all bombs" fired on Islamic State forces in Afghanistan carried a chilling message for North Korea.
According to The Daily Star, former US officer James Peek said he believed the launch of the mega bomb was meant to frighten North Korea.
"We are entering what perhaps might come close to a showdown between the US and the north," he told the Daily Star.
He told the news agency that the bomb would have been fired at strongholds in Syria or Iraq if it were meant to destroy Islamic State.
"Instead, this bomb was meant for North Korea. It was designed during the Iraq War as a means to penetrate destroy underground nuclear facilities," he told the Daily Star.
However the Afghan Ministry of Defence reported 36 ISIS militants were killed in the US attack.
US President Donald Trump boasted about the bombing during a press conference in Atlanta on Thursday.
"Everybody knows exactly what happened. What I do is I authorise my military. We have the greatest military in the world and they've done a job as usual," he said.
"We have given them total authorisation and that's what they're doing and frankly that's why they've been so successful lately.
"If you look at what's happened over the last eight weeks and compare that really to what's happened over the past eight years, you'll see there's a tremendous difference, tremendous difference.
"So we have incredible leaders in the military, and we have incredible military. We are very proud of them. This was another very, very successful mission."
White House press secretary Sean Spicer said all appropriate measures were taken to avoid civilian casualties. The military is doing a damage assessment, so casualty figures were not immediately clear.
"We must deny them operational space, which we did," Spicer said.
General John Nicholson, commander of US forces in Afghanistan, signed off on the use of the bomb, according to sources.
The bomb was rapidly developed in 2002-2003 around the time of the US-led invasion of Iraq.
According to the air force, the last time the MOAB was tested in 2003, a huge mushroom cloud could be seen from 32 kilometres away.
President Trump during the campaign promised to "bomb the s**t" out of IS, and this escalation could be the first sign of that policy in action.
