The Pentagon says US forces have dropped what they claim is their largest ever conventional bomb.

Containing 11 tons of explosives, it was targeted on a cave complex used by Islamic State fighters in the country, close to the border with Pakistan.

The so-called GBU-43 is also named the Massive Ordnance Air Blast bomb.

White House Press Secretary Sean Spicer says the attack is a blow to ISIS, and says US forces made every effort to prevent civilian casualties.

.@PressSec Sean Spicer: "We targeted a system of tunnels and caves that ISIS fighters used to move around freely" https://t.co/XSrBMHv8a5 pic.twitter.com/dTmbfeq89s

— POLITICO (@politico) April 13, 2017