US military officials said the Massive Ordnance Air Blast bomb - dubbed the "mother of all bombs", the largest non-nuclear weapon ever used in combat - targeted an underground network of caves and tunnels that Islamic State fighters had used for weeks to evade an ongoing operation by USA and Afghan forces.
The statement said it is the responsibility of Afghans, not the U.S., to remove Islamic State from the country.
President Donald Trump said this week he would be sending his new national security adviser, Lt. Gen. HR McMaster, to Afghanistan "to find out how we can make progress alongside our Afghan partners and North Atlantic Treaty Organisation allies".
A senior American officer said the bomb was the right weapon for the job while an Afghan officer said that before the strike, joint forces had been unable to penetrate the region.
The death toll from Thursday's attack was initially put at 36.
A general view of Achin district, in Jalalabad, after USA forces dropped Thursday the bomb, Afghanistan.
The mountain fortress, located in the Achin district of Afghanistan, was reportedly heavily fortified and extremely hard for ground forces to reach, according to Afghan Gen. Daulat Waziri, spokesman for the Afghanistan Ministry of Defense.
"This weapon was used against Isis-K and their sanctuary inside Afghanistan", NATO forces commander General John Nicholson said., according to the AP.
No civilians were injured in the raid, which took place in the Mohmand Dara village, Asadkhil area of the district, the statement added.
According to the Department of Defence, there are about 600- 800 ISIS-Khorasan fighters in the area where the bomb was dropped.
Afghanistan's Defense Ministry reported on April 14 that 36 IS fighters had been killed in the bombing in Achin district, which targeted a tunnel complex used a as a command center and ammuntions depot by the IS which had been mined against conventional ground attacks.
Others, including the former President Hamid Karzai, the Taliban, and the Afghan Ambassador to Pakistan Hazrat Ummer Zakhilwal, have denounced this massive display of power. "The strike was created to minimize the risk to Afghan and U.S. Forces conducting clearing operations in the area while maximizing the destruction of ISIS-K fighters and facilities", said the US Force.
The GBU-43's nickname is based on the acronym used by the US Air Force, which calls it the Massive Ordnance Air Blast bomb.
The strike was part of a joint operation by Afghan and global troops, Afghan President Ashraf Ghani's office said in a statement.
Nicholson said the US conducted "persistent surveillance over the area before during and after the operation" and that there had been no evidence of civilians hit in the strike.
"This is the right weapon against this target".