The White House has expressed doubts over North Korean leader Kim Jong-un's claim that the country had developed hydrogen bomb.
According to News.com.au, White House spokesperson Josh Earnest said that they are concerned about North Korea's "destabilising actions" but added that available information "calls into serious question" on 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."
Earlier, North Korea has tested three atom bombs, which rely on nuclear fission.
Kim said in a speech marking the 70th anniversary of the founding of the ruling communist Workers' Party on October 10, that he is prepared to wage war against the US if necessary.