Last Updated Jan 6, 2016 3:40 PM EST
U.S. intelligence is "highly skeptical" that North Korea actually detonated a thermonuclear device in spite of claims that it conducted a hydrogen bomb test, CBS News Pentagon Correspondent David Martin reported.
The rogue nation said Wednesday that it tested a "miniaturized" hydrogen bomb, which, if confirmed, would represent a major improvement to their nuclear arsenal.
In response to the announcement, the Security Council pledged Wednesday to swiftly pursue new sanctions against North Korea, strongly condemning its latest nuclear test as a "clear violation" of previous U.N. resolutions.
"In the press statement issued after the Security Council met, the 15-member Council "strongly condemned" the North Korean test as a violation of four resolutions and promised to "begin work immediately" on a new, presumably tougher, measure," reports CBS News' Pamela Falk, who was in South Korea in May with the U.N. Secretary General, when his trip to North Korea was cancelled.
Ambassador Samantha Power said, "The international community must impose real consequences for the regime's destabilizing actions, and respond with steadily increasing pressure. The Security Council has a key role to play in holding North Korea accountable by imposing a tough, comprehensive, and credible package of new sanctions, and by ensuring rigorous enforcement of the resolutions it has already adopted. The Security Council's commitment today to impose "further significant measures" in a new resolution marks an important step in that process."
The sanctions would be the fifth round imposed on North Korea since the country's first nuclear test in 2006. The sanctions are aimed at reining in the North's nuclear and missile development, but Pyongyang has ignored them and moved ahead with programs to modernize its ballistic missiles and nuclear weapons.
The Security Council held an emergency meeting after North Korea announced its first hydrogen bomb test, which would mark a major advance for its still-limited nuclear arsenal.
The Security Council said North Korea's actions were a "clear violation" of the four previous sanctions resolutions "and therefore a clear threat to international peace and security continues to exist."
The U.N.'s most powerful body said it had pledged to take "further significant measures" - U.N. code for sanctions - in the event of another test and would begin work immediately on a new sanctions resolution in light of "the gravity of this violation."
Despite North Korea's boasting, the intelligence communities in both the U.S. and South Korea estimated that the blast was in the single digit kilotons, whereas a thermonuclear device would actually be measured in megatons. North Korea might have been testing the nuclear trigger for a thermonuclear device or the test could have been a failure.
It also could have been another nuclear test, but the U.S. will not be able to confirm either way until aircraft sample the air for isotopes.
U.S. intelligence had expected a test at some point, based on the amount of activity at the test site, but it had no warning that the test was about to occur.
CBS News Correspondent Seth Doane reported that the test took North Korea's neighbors by surprise. It set off an explosion that registered a Magnitude 5.1 earthquake, although it quickly became clear that the seismic activity might have been set off by something man made.
Defense Secretary Ash Carter spoke with his South Korean counterpart, Han Min-koo, by phone Wednesday to discuss potential responses. The two agreed that a test would violate international law and threaten the peace and stability of the entire Asia-Pacific region, Pentagon Press Secretary Peter Cook said in a statement.
The two defense officials also reaffirmed that the international community will not accept North Korea as a nuclear state.
The mere claim of a hydrogen bomb test was enough to prompt the United Nations Security Council to call an unscheduled, closed-door meeting, to take place at U.N. headquarters in New York on Wednesday.
CBS News foreign affairs analyst Pamela Falk warned, however, that the U.N. has limited options to try and control the rogue government of Kim Jong Un.
The Security Council could decide to increase sanctions against the North Korean regime, notes Falk, but "that, to date, has not worked to slow the nuclear program in Pyongyang."