White House says it doubts NKorea H-bomb claims

The White House on Thursday poured cold water on leader Kim Jong-Un's suggestion that North Korea has developed a hydrogen bomb.

Spokesman Josh Earnest said the White House had concerns about the "destabilizing actions" of the regime, but said available information "calls into serious question" claims that Pyongyang has a thermonuclear device.

During a recent inspection tour of a historical military site, Kim mentioned that North Korea was already a "powerful nuclear weapons state ready to detonate self-reliant A-bomb and H-bomb to reliably defend its sovereignty," the North's official KCNA news agency said Thursday.

North Korea has already tested three atom bombs, which rely on nuclear fission.

A hydrogen, or thermonuclear, device uses fusion in a chain reaction that results in a far more powerful explosion.