A report by the North's official Korean Central News Agency said the country is now a "powerful nuclear weapons state ready to detonate a self-reliant A-bomb (atomic bomb) and H-bomb (hydrogen bomb) to reliably defend its sovereignty and the dignity of the nation," Yonhap reported.
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Thermonuclear bombs, or hydrogen bombs, are far more powerful than conventional nuclear weapons.
It is believed to be the first time Kim has publicly said the North has developed the weapon, Yonhap reported.
Kim said he is prepared to wage war against the United States if necessary in a speech to mark the 70th anniversary of the founding of the ruling communist Workers' Party on Oct. 10.