Shortly before the commission issued its declaration, U.S. envoy on North Korea Glyn Davies urged Pyongyang not to explode an atomic device.
"Whether North Korea tests or not, it's up to North Korea. We hope they don't do it. We call on them not to do it," he told reporters in Seoul after meeting with South Korean officials. "It will be a mistake and a missed opportunity if they were to do it."
Davies was in Seoul on a trip that includes stops in China and Japan for talks on how to move forward on North Korea relations.
White House spokesman Jay Carney on Thursday said North Korea's aggressive stance is unnecessary and warned against any further testing.
"North Korea's statement is needlessly provocative and a test would be a significant violation of United Nations Security Council resolutions. Further provocation would only increase Pyongyang's isolation, and its continued focus on its nuclear and missile program is doing nothing to help the North Korean people."
He said the recent U.N. resolution is a "strong message of the international community's opposition to North Korean provocations and these tightened sanctions will impede the growth of weapons of mass destruction programs in North Korea and the United States will be taking additional steps in that regard."
Carney did not elaborate on what those steps might be.