The US dropped a massive GBU-43 bomb, the largest non-nuclear bomb it has ever used in combat, in eastern Afghanistan on Thursday against a series of caves used by Islamic State militants, a report said.

It was the first time the United States has used this size of bomb in a conflict, reported Sydney Morning Herald.

It was dropped from a MC-130 aircraft in the Achin district of Nangarhar province, close to the border with Pakistan, Pentagon spokesman Adam Stump said.

General John Nicholson, the head of US and international forces in Afghanistan, said the bomb was used against caves and bunkers housing fighters of the Islamic State in Afghanistan, also known as ISIS-K.

It was not immediately clear how much damage the device did.

White House spokesman Sean Spicer opened his daily news briefing speaking about the use of the bomb and said, "We targeted a system of tunnels and caves that ISIS fighters used to move around freely, making it easier for them to target US military advisers and Afghan forces in the area."

The Pentagon said in its statement that "US Forces took every precaution to avoid civilian casualties with this strike."

He said the bomb was used at around 7pm local time and described the device as "a large, powerful and accurately delivered weapon." The US took "all precautions necessary to prevent civilian casualties and collateral damage," he said.