Washington - The United States dropped "the mother of all bombs," the largest non-nuclear device it has ever unleashed in combat, on a network of caves and tunnels used by Islamic State in eastern Afghanistan on Thursday, the military said.

US President Donald Trump touted the bombing as evidence of a more muscular US foreign policy since he took office in January after eight years of President Barack Obama.

The 21,600 pound (9,797 kg) GBU-43 bomb, which has 11 tons of explosives, 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.

The GBU-43, also known as the "mother of all bombs", is a GPS-guided munition and was first tested in March 2003. It is regarded as particularly effective against clusters of targets on or just underneath the ground. Other types of bombs can be more effective against deeper, hardened tunnels.

It was the first time the United States has used this size of conventional bomb in a conflict.

Trump described the bombing as a "very successful mission". It was not immediately clear how much damage the device did.

During last year's presidential election campaign, Trump vowed to give priority to destroying Islamic State, which operates mostly in Syria and Iraq. He flexed US military muscles last week by ordering a cruise missile attack on a Syrian government airbase in retaliation for a poison gas attack.

"If you look at what's happened over the last eight weeks and compare that really to what's happened over the last eight years, you'll see that there's a tremendous difference", Trump told reporters at the White House on Thursday.

The security situation remains precarious in Afghanistan, with a number of militant groups trying to claim territory more than 15 years after the US invasion which toppled the Taliban government.

Last week, a US soldier was killed in the same district as where the bomb was dropped while he was conducting operations against Islamic State.

White House spokesman Sean Spicer said the bombing "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."

Spicer said the bomb was dropped at around 7 pm local time and described it as "a large, powerful and accurately delivered weapon". US forces took "all precautions necessary to prevent civilian casualties and collateral damage".

(China Daily USA?04/14/2017 page1)