A Security Council diplomat says the U.N.'s most powerful body is working on a resolution that would impose tougher sanctions on North Korea to reflect its claim that it tested a powerful hydrogen bomb, even if the claim proves to be untrue.

The diplomat, speaking on condition of anonymity Wednesday because consultations have been private, says the North's claim that it tested a hydrogen bomb last week represents "a step change," and the council needs to show that its response also represents "a step change."

The diplomat says all 15 council members agree that North Korea should be denuclearized.

The council has strongly condemned the test as a "clear violation" of previous U.N. resolutions.

There is widespread skepticism over the H-bomb claim, which would mark a major advance for Pyongyang.