'Mother of all bombs' video: Footage shows US dropping biggest non-nuclear bomb on Isis in Afghanistan

Afghan military says 36 Islamic State fighters died in the blast

The Pentagon has released footage of the moment the biggest non-nuclear bomb to be dropped in combat hit Afghanistan.

Afghan military officials said 36 Isis fighters died when the US dropped the "the mother of all bombs" – the GBU-43 Massive Ordnance Air Blast Bomb (MOAB).

The US Department of Defense posted a video of the strike on Twitter with the caption: "A MOAB bomb strikes Isis cave and tunnel systems in eastern Afghanistan.

"The strike was designed to minimise risk to Afghan and US forces."

The monochrome aerial footage shows the moment the blast hit a mountainous area, with a dark black cloud ballooning from its point of explosion.

The US commander in Afghanistan said the MOAB bomb, dropped on an area to the east of the country known to be populated by Isis-affiliated militants, had "achieved its intended purpose".

"This weapon was used against Isis-K and their sanctuary inside Afghanistan," General John Nicholson, commander of Nato forces, told reporters. "The purpose of this operation was to eliminate their sanctuary inside Southern Nangarhar... The weapon achieved its intended purpose."

A member of Afghan security points to the mountainous area where the US dropped a MOAB bomb targeting Isis caves in Nangarhar province, Afghanistan (EPA/GHULAMULLAH HABIBI)

Meanwhile, Pentagon officials have said the US commander in Afghanistan who ordered use of the warhead did not need and or request Donald Trump's approval.

The officials said that even before Mr Trump took office in January, Gen. Nicholson had standing authority to use the bomb.

Isis-K is an affiliate of the extremist Islamic State group, also present inside Iraq and Syria.

During his presidential campaign, Donald Trump said if elected he would "bomb the s**t out of Isis".

Designed in 2002, the MOAB, which weighs around 10,000 kilograms, is one of the most powerful conventional weapons in existence.

The radius of its blast stretches around a mile, Rob Farley, a University of Kentucky professor who studies the US Air Force, told Vox.

"That does not mean everything within a mile dies – it means that everything within a mile has a potential to be affected," he said.

Its explosion is equivalent to 11 tons of TNT. The 'fat man' nuclear bomb that was dropped on Nagasaki in 1945 was much more powerful, releasing energy equivalent to 21 kilotons of TNT.

Bill Riggio, of the Foundation for Defence of Democracies think tank, described how the MOAB, a precision weapon used on softer targets, such as cave systems, works.

"What it does is basically suck out all of the oxygen and lights the air on fire," he told the Air Force Times. "It's a way to get into areas where conventional bombs can't reach."

The mission had been in the planning stages for months, the Pentagon said in a statement.

However, they said they “did not have the information” on whether the mission was being planned during the previous Obama administration.