A top Pentagon official has said the only sure way of eliminating North Korea's nuclear weapons capabilities would be by putting U.S. boots on the ground — a move that some worry could prompt Pyongyang to use biological, chemical and even nuclear weapons against Japan and South Korea.

"The only way to 'locate and destroy — with complete certainty — all components of North Korea's nuclear weapons programs' is through a ground invasion," Rear Adm. Michael J. Dumont, vice director of the Joint Chiefs of Staff wrote in a blunt assessment to U.S. lawmakers that was released Saturday on the realities of reining in Pyongyang's nuclear ambitions.

Dumont's letter came in response to questions by U.S. Reps. Ted Lieu of California and Ruben Gallego of Arizona in regards to military planning and casualty estimates in the event of conflict with the nuclear-armed North.