The strike on Thursday hit an IS mountain hideout in a remote area of Nangarhar province, in eastern Afghanistan, near the Pakistan border.
It was the first time the US military had unleashed the GBU-43/B Massive Ordnance Air Blast bomb, its largest non-nuclear bomb, in combat.
IS issued a statement through its propaganda agency Amaq, saying: “Security source to Amaq agency denies any dead or wounded from yesterday’s American strike in Nangarhar using a GBU-43/B.”
But Nangarhar Province spokesman Attaullah Khogyani said 90 IS fighters had died, while Achin district governor Esmail Shinwari said “at least 92 Daesh (another name for IS) fighters were killed in the bombing”.
There were “no military and civilian casualties at all”, Mr Shinwari added.
The top US military commander in Afghanistan said the decision to deploy one of the largest conventional bombs ever used in combat, which Pentagon officials described as the “mother of all bombs”, was purely tactical.
“This is the right weapon for the right target,” said US General John W Nicholson, the NATO commander in Afghanistan.
The attack, in an area that had seen heavy fighting in recent weeks between Afghan forces and IS militants, destroyed several IS caves and ammunition caches, the Afghan defence ministry said.
A ministry spokesman, General Daulat Waziri, said the bombing was necessary because the tunnel complex was extremely hard to penetrate, with some tunnels as deep as 40m.
“It was a strong position and four times we had operations (attacking the site) and it was not possible to advance,” he said, adding that the road leading to the complex “was full of mines”.
The 21,600lb (9,797kg) GBU-43 bomb, which was dropped from an MC-130 aircraft, has the explosive power of 11 tons of TNT.
The bombing left villagers terrified on both sides of the Afghan-Pakistani border.
In the Afghan village of Achin, just a few miles from where the bomb hit, Palstar Khan said: “Last night’s bomb was really huge, when it dropped, everywhere, it was shaking.”
Some in Pakistan said the explosion was so loud they thought a bomb had been dropped in their village.
“I was sleeping when we heard a loud explosion. It was an earsplitting blast,” said Shah Wali, 46, who lives nine miles from the border.
“I jumped from my bed and came out of my home to see what has gone wrong in our village.”
The US believes there are between 600 and 800 IS fighters in Afghanistan, mostly in Nangarhar.
President Donald Trump praised the US military for carrying out what he called a “very, very successful mission”.
He is preparing to dispatch his first high-level delegation to the Afghan capital Kabul, amid uncertainty about his plans for the nearly 9,000 American troops stationed in Afghanistan.