The Pentagon says it used the bomb on a cave complex believed to be used by the so called "Islamic State" (IS) on Thursday evening.

Pentagon spokesman Adam Stump said it was the first time the GBU-43/B Massive Ordnance Air Blast Bomb, which is GPS-guided and contains 11 tons of explosives, was dropped.

Read: What makes MOAB the 'Mother of all bombs'?

The target was a "system of tunnels and caves used by IS to move around freely," according to White House Press Secretary Sean Spicer. The bomb fell in the Achin district of the Nangarhar province of eastern Afghanistan, close to the border with US ally Pakistan.

"The strike was designed to minimize the risk to Afghan and US forces conducting clearing operations in the area while maximizing the destruction of ISIS-K fighters and facilities," according to a statement from the Pentagon referring to an alternate acronym for IS.

Read: 'Mother of all bombs' what has it achieved?

On Friday, Afghan officials said the bomb hit intended IS targets, avoiding civilian casualties.

"As a result of the bombing, key Daesh (IS) hideouts and a deep tunnel complex were destroyed and 36 IS fighters were killed," the defense ministry stated.

The figure was updated on Saturday by Achin district governor Esmail Shinwari who said "At least 92 Daesh (IS) fighters were killed in the bombing," using an alternative name for IS. Shinwari insisted there were "no military and civilian casualties at all."

Watch video 00:35 36 'IS' militants killed in US bombing, says Kabul

'A brutal misuse'

Former Afghan president Hamid Karzai criticized the use of such a weapon on his country's soil.

"This is not the war on terror, but the inhuman and most brutal misuse of our country as testing ground for new and dangerous weapons," he said on Twitter.

His successor, President Ashraf Ghani issued a statement saying that the strike was part of a joint operation between Afghan and international troops.

"Afghan and foreign troops closely coordinated this operation and were extra cautious to avoid any civilian casualties," it said.

Top American US military commander in Afghanistan, General John Nicholson, also defended the strike at a press conference in Kabul on Friday, calling the decision to use the bomb a purely tactical decision.

"This was the right weapon for the right target," said General Johnson according to Reuters.

The spokesperson for affected Nangahar province Ataullah Khogianai further explained that the decision to use the bomb came about after numerous operations against IS had been hindered by militants' large hidden bunker system.

"Important IS fighters had entrenched themselves there. These bunkers were therefore very dangerous because they would carry kidnapped locals here," Khogianai told DW.

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The bomb produces a mushroom cloud that can be seen from miles around

Huge explosion

Eyewitnesses described the bomb's fiery landing in the Momand Dara area of the Achin district.

"The place [where the bomb landed] was on fire for nearly half an hour," local Achin resident Malek Yunes told DW. "No civilians live where the bomb was thrown...but in the flat area lower down there are towns. We cannot go there due to ISIS."

"The place has been turned on its head [destroyed]," Yunes added.

Achin district governor Esmail Shinwari likewise described an outpouring of flames in the mountainous area.

"The explosion was the biggest I have ever seen. Towering flames engulfed the area," Shinwari told AFP.

US President Donald Trump said Thursday's bombing was "another very, very successful mission." Trump would not say if he authorized the use of the bomb, or if it was a message to North Korea.

Read: North Korea warns of nuclear strike against US if aggression continues

The US estimates there are between 600 and 800 IS fighters in Afghanistan, primarily in the Nangarhar province. The US is also working with Afghan forces to fight the Taliban.

The US military first tested the bomb in March 2003. According to the US Air Force, the last time the bomb was tested it created a mushroom cloud that could be seen from 20 miles (32 km) away.

kbd/rt (AP, AFP, Reuters)