The top U.S. commander in Afghanistan did not ask permission from the president before he ordered a massive conventional bomb to be dropped on a complex of tunnels used by ISIS fighters in a remote mountain region along the border with Pakistan, a senior defense official said Friday.

The GBU-43/B MOAB or massive ordnance air blast bomb, informally dubbed, the “Mother of All Bombs,” is the largest non-nuclear bomb ever used in combat by the United States.