North Korea called it a hydrogen bomb and said the test "scientifically proved the power of the smaller H-bomb," though the United States and others expressed skepticism that Pyongyang actually tested a hydrogen bomb for the first time. Nonetheless, whatever the North detonated underground will likely push the country closer toward a fully functional nuclear arsenal, which it still is not thought to have.

A Security Council diplomat said Wednesday that the U.N.'s most powerful body is working on a resolution that imposes tougher sanctions on North Korea to reflect the claim that it tested a more powerful hydrogen bomb, which is "a step change" from its three previous atomic test.

The diplomat, speaking on condition of anonymity because consultations have been private, said all 15 council members agree that North Korea should be denuclearized, and this will be reflected in a new resolution.

North Korea's U.N. mission circulated a report from the country's news agency saying the Jan. 6 test wasn't to "threaten" or "provoke" anyone but was indispensable to build a nuclear force "to cope with the U.S. ever-more undisguised hostile policy" toward the Democratic People's Republic of Korea, the country's official name.

It said North Korean scientists and technicians "are in high spirit to detonate H-bombs ... capable of wiping out the whole territory of the U.S. all at once as it persistently moves to stifle the DPRK."