North Korea's U.N. mission claimed Wednesday that its successful nuclear bomb test showed that it could now "wipe out" the United States, as the U.N. Security Council grappled with a response to the underground blast.

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.

Former Los Alamos National Laboratory director Siegfried Hecker, one of the world's top experts on North Korea's nuclear program, said last week he did not believe it tested "a real hydrogen bomb." But Hecker, who has visited the North seven times since 2004, said in an interview with Stanford University's Center for International Security and Cooperation, that the most worrisome result of the test is that North Korea "will have achieved greater sophistication in their bomb design."

There was no immediate response to a request for comment from the U.S. mission to the United Nations. The Security Council last approved sanctions against North Korea three weeks after its third nuclear test on Feb. 12, 2013. That resolution was largely negotiated by the United States and China, North Korea's traditional ally.