OFFUTT AIR FORCE BASE, Neb. (AP) — The top commander of U.S. nuclear forces says he assumes the Sept. 3 nuclear test by North Korea was a hydrogen bomb.

Air Force Gen. John E. Hyten, commander of Strategic Command, told reporters that while he was not in a position to confirm it, he assumes from the size of the underground explosion and other factors that it was a hydrogen bomb — which is a leap beyond the fission, or atomic, bombs North Korea has previously tested.

North Korea claimed they exploded a hydrogen bomb, and while U.S. officials have not contradicted them, they have not confirmed it, either.

Hyten says a North Korean H-bomb is worrying because of the scale of destruction it could cause if used in war.