On it's website, the Pentagon writes "U.S. Forces Afghanistan conducted a strike on an Islamic State of Iraq and Syria-Khorasan tunnel complex in Achin district, Nangarhar province, Afghanistan, as part of ongoing efforts to defeat ISIS-K in Afghanistan. The strike used a GBU-43/B Massive Ordnance Air Blast bomb dropped from a U.S. aircraft. The strike was designed 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."
Army General John W. Nicholson, commander of U.S. Forces Afghanistan says “as ISIS-K’s losses have mounted, they are using [improvised bombs], bunkers and tunnels to thicken their defense. This is the right munition to reduce these obstacles and maintain the momentum of our offensive against ISIS-K.”
Reports from Afghan sources say 36 Islamic state fighters were killed. They report no civilian casualty's.