N. Korea's H-Bomb Claim Rattles Neighbors' Nerves

North Korea said Wednesday that it had conducted an underground test of a Hydrogen bomb. If confirmed, it would be North Korea's fourth nuclear test, and a hydrogen bomb would be a significant leap forward in North Korea's efforts to advance its nuclear arsenal.

The claimed test has sparked widespread condemnation.

CBS News correspondent Seth Doane says North Korea's neighbors in the region were taken by surprise. At first the reports were of an earthquake, but it quickly became apparent that the seismic event was quite possibly man-made.

North Korea claimed its first-ever test of a miniaturized hydrogen bomb was a "perfect success" in a state TV broadcast. The North took aim at the U.S., calling the test a self-defense measure.

The explosion, which registered as a Magnitude 5.1 earthquake, struck near the Punggye-ri site, where the North carried out nuclear tests in 2006, 2009, and 2013.

Photos today showed North Koreans cheering the news while, across the border in South Korea, citizens watched nervously. In media reports, South Korea's military cast doubt on whether the explosion was big enough to be a hydrogen bomb.

The North is infamous for its sabre-rattling, but a hydrogen bomb would be a major advance in technology; they are much more powerful and more difficult to make than an atomic bomb.

North Korean TV showed what appeared to be a personal note from leader Kim Jong Un signing-off on the hydrogen bomb test on December 15.

Doane was in North Korea in October with a CBS News team, and then it appeared relations with China -- its biggest ally -- were warming. China sent a top government official to the military parade CBS News attended.

But today, China joined neighbors in the region in strong condemnation of the nuclear test.

Asked by Doane whether China was likely to move past rhetoric and take any action over the North's latest move, Ministry of Foreign Affairs spokeswoman Hua Chunying noted that China had "been making active efforts towards the goal of peninsula denuclearization -- in words and actions."

"It requires efforts from all parties," added Hua.

The White House has said it could be days before the U.S. can determine definitively whether it was indeed a hydrogen bomb detonated by North Korea.

CBS News national security analyst Juan Zarate, who studied North Korea as a deputy national security adviser to President George W. Bush, told "CBS This Morning" that if it was a hydrogen bomb, it could be a "game changer" for the West.

"If it was a hydrogen bomb, that will demonstrate a technological leap forward for North Korea," Zarate said. "If they are on the verge of miniaturization," as claimed by the North Koreans, "that means that they're very close to being able to put that on a warhead and potentially deploy it well beyond the Korean peninsula."

Zarate noted, however, that while the North has been working to develop it's ballistic missile capabilities, "analysts don't think that these have reached the stage of being successful missile programs. But they are advancing."

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 warns, 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."