Qari Mehrajuddin first saw "lightning like a thunder storm" followed by the roar of an explosion, an all-to-familiar sound for residents in Afghanistan's war-torn Nangarhar province.

"I thought there was a bombing just outside my home," he said.

In reality, the blast was around three miles away, its massive impact bigger than any before seen in the region.

On Thursday night, American forces dropped one of the largest conventional bombs ever used in combat on what they described as a tunnel complex used by Daish militants in Nangarhar's Achin district.

Achin is separated from Pakistan by a range of high mountains, one of the areas where Taliban and al Qaeda fighters fled when the United States first intervened in the country in late 2001.

Now U.S. officials say militants affiliated to the Middle East-based Islamic State network have begun fortifying caves in the region in an effort to hold off joint operations by Afghan and U.S. forces.

Some residents in areas of Achin recently liberated from Daish occupation welcomed Thursday's strike, which hit headlines around the world and has been widely interpreted as a deliberate show of strength by U.S. President Donald Trump.

"If you want to destroy and eliminate Daish, then even if you destroy my home we won't complain, because they are not human beings, they are savages," said resident Mir Alam Shinwari, using an Arabic term for Islamic State.

Shinwari described a litany of abuses he said were committed by Islamic State fighters.

"They used to marry our daughters and wives to their fighters, blamed residents for spying, they beheaded, cut (off) hands and did not allow mobile phones that had cameras," he told Reuters.

That sentiment was echoed by Gul Sher, another resident who called on the United States and the Afghan government to "hit Daish and wipe them out completely."

"We were so fed up with the atrocities of Daish and they were against everything we are," he said.

Away from the area directly impacted by the blast, the reaction was more mixed.

"The fact is that America used their big bomb here to test its effectiveness," said Kabul resident Asadullah Khaksar. "If America wants to eliminate Daish, it is very easy because they created this group."

Rahim Khan, another Kabul resident, also took a skeptical view of America's role in the fighting.

"If this bombing was indeed for the elimination of Daish this is a good move, but I don't believe it," he said. "This is all imposed on Afghanistan for proxy war."

Some Afghans remain deeply suspicious of Washington's motives in sending troops to the country more than 15 years ago, and view their ongoing presence as a form of occupation.

Others are glad of their intervention, fearing that the alternative would be a return to the strict Islamist rule of the Taliban, ousted from power in 2001 but fighting a stubborn insurgency that is costing thousands of lives every year.

Defending his decision to deploy the bomb, General John Nicholson, top U.S. commander in Afghanistan, called Islamic State fighters "animals" for conducting attacks against targets like a hospital in Kabul.

"The Afghan army, and specifically their commandos, are leading the fight against these barbaric terrorists," he told journalists in Kabul on Friday.

"They're doing it on behalf of the people of Afghanistan and indeed, they are doing it on behalf of all of us."