The executive arm of the United Nations has pledged new measures in response to North Korea’s fourth nuclear test even as weapons experts and the White House dispute the regime’s claims to have successfully detonated a hydrogen device far more powerful than an atomic bomb. The hostile act has drawn international condemnation from nations including Russia, Japan and the U.S. If the test was of a hydrogen weapon, North Korea would join a small group of nations, including the U.S. and China, known to possess the capability. U.S. officials have previously said it was unlikely the regime could have developed a hydrogen bomb, and have also challenged its claims it was capable of miniaturizing a nuclear device to mount it on a missile. North Korea says its rockets can reach parts of the U.S.