Media playback is unsupported on your device Media caption The moment the MOAB bomb struck the IS cave and tunnel system

At least 90 militants from the Islamic State (IS) group were killed by a huge bomb dropped by the US in Afghanistan, a regional governor says.

The most powerful non-nuclear bomb ever used by the US in combat was dropped on an IS base in Nangarhar province.

A network of tunnels and caves was destroyed on Thursday evening local time, US officials said.

The death toll was confirmed to the BBC by Ismail Shinwary, the governor of Achin province within Nangarhar.

IS had earlier said it had not suffered any casualties in the blast.

No civilians were killed in the explosion, Mr Shinwary said. The Chief Executive of Afghanistan, Abdullah Abdullah, said the attack had been carried out in co-ordination with his government and "great care had been taken to avoid civilian harm".

However, one resident close to where the blast happened told the BBC some homes were destroyed. The explosion lit up the whole night sky, he said.

Known as the "mother of all bombs", or MOAB, the device was dropped on Thursday evening by an MC-130 transport plane, falling in Nangarhar's Achin district.

It was the first time the bomb, one of only 15 ever built, had been used in combat.

Media playback is unsupported on your device Media caption Watch 2003 footage of the GBU-43/B Massive Ordnance Air Blast Bomb (MOAB) being tested

When IS announced the establishment of its Khorasan branch - an old name for Afghanistan and surrounding areas - in January 2015, it was the first time the group had officially spread outside the Arab world.

"The enemy had created bunkers, tunnels and extensive mine fields, and this weapon was used to reduce those obstacles so that we could continue our offensive in southern Nangarhar," said Gen John Nicholson, the most senior US military commander in Afghanistan.

While the attack was supported by the Afghan government, former president Hamid Karzai said it represented an "inhuman and most brutal misuse of our country as testing ground for new and dangerous weapons".

Mr Shinwary had earlier confirmed to the BBC that Afghan special forces, with the help of American air support, had begun anti-IS operations in the area two weeks ago.

But reports say fighting has intensified in recent days. Last Saturday, an American special forces soldier was killed fighting militants.