North Korea says it successfully conducts hydrogen bomb test

(CNN) — Sticking it to its foes, North Korea on Wednesday celebrated what it called a successful hydrogen bomb test — a milestone that, if true, marks a colossal advancement for the reclusive regime and a big test for leaders worldwide to determine what to do about it.

“Make the world … look up to our strong nuclear country and labor party by opening the year with exciting noise of the first hydrogen bomb!” read a document signed by North Korean leader Kim Jong Un on state television.

Pyongyang has been very vocal about its nuclear ambitions, pressing on despite widespread condemnation, sanctions and other punishments. Having a hydrogen bomb — a device far more powerful than the plutonium weapons that North Korea has used in three earlier underground nuclear tests — ups the ante significantly.

Still, is this boast legitimate? The purported underground test, which happened at 10 a.m. (8:30 p.m. ET Tuesday), corresponded with a magnitude 5.1 seismic event centered 12 miles (19 kilometers) east-southeast of Sungjibaegam, according to the U.S. Geological Survey. That’s comparable to readings from North Korea’s most recent plutonium test in 2013.

Norsar, a Norway-based group that monitors nuclear tests, noted both facts and estimated, based on the seismic readings, a blast equivalent to less than of 10,000 tons of TNT — smaller than those of the atomic bombs used on Hiroshima and Nagasaki, and far less than thermonuclear weapons that typically are as potent as millions of tons of TNT.

“We won’t know for another few days or weeks whether this was (a hydrogen bomb),” said Martin Navias, a military expert at King’s College London. “It doesn’t look like one; … one would have expected it to be greater if it was an H-bomb.”

An answer may be found in U.S. or South Korean analysis of the atmosphere for “trace elements [of] radiation,” though Mike Chinoy, a fellow at the University of Southern California’s U.S.-China Institute, noted that “we may never know 100%.”

Count Bruce Bennett, a senior defense analyst with the nonpartisan research group, among the skeptics. He said North Korea has had trouble “mastering even the basics of a fission weapon,” so it’s a big leap to think it could create an even more complicated hydrogen bomb.

“Unless North Korea has help from outside experts, it is unlikely that it has really achieved a hydrogen/fusion bomb since its last nuclear test,” Bennett said.

U.N. Security Council to convene meeting

Whether or not it’s true, North Korea’s claim — which Kim hinted was coming a few weeks ago — got the world’s attention. And that may be Pyongyang’s main aim.

“If there’s no invasion on our sovereignty, we will not use nuclear weapon[s],” North Korea’s state news agency reported. “This H-bomb test brings us to a higher level of nuclear power.”

The United Nations Security Council held a closed-door meeting midday Wednesday on this topic at the request of the United States and Japan. The question is: What can be done, and will it make a difference?

Past U.N. resolutions have included arms, nonproliferation and luxury good embargoes, a freeze on overseas financial assets and a travel ban. None of these have stopped North Korea from continuing its nuclear program.

“The sanctions are clearly quite leaky,” said Victor Cha, a Georgetown University professor and National Security Council’s Asian affairs director during the George W. Bush administration. “If you had to [find one reason], you’d have to point to China. They [have] not [been] willing to really step on the North Koreans’ necks to get them to give up these weapons.”

China did speak out strongly against the latest test, pointing out it had no advance notice. Beijing had company, as leaders from around the world, including Russia and NATO, condemned it — a rare show of unanimity at a time of pervasive discord on issues like Syria’s civil war, the Shiite-Sunni Muslim divide, Ukraine and migration.

The anger and danger were felt most in South Korea, which was split from the North seven decades ago.

“This is clearly a provocation and threatening the lives of people and safety,” South Korean President Park Geun-hye said. “We have been continuously warning that [North Korea] will pay a price for conducting a nuclear test.”

Test puts U.S. ‘on the spot’

Pyongyang singled out the United States — or, as it called it, “a gang of cruel robbers” and “hideous nuclear criminal that has constantly posed nuclear blackmail for more than 70 years, seriously endangering mankind” — in its highly charged official reports around the time of the test announcement.

North Korea not only has a “legitimate right” to have nuclear weapons, they’re needed as a deterrent to Washington’s “deep-rooted, harsh and … hostile policy,” according to these reports.

“The spectacular success … in the H-bomb test [is] a historic event of … national significance as it surely guarantees the eternal future of the nation,” the KCNA story stated.

Chinoy pointed out that three of North Korea’s four nuclear tests — in 2009, 2013 and now — have taken place during the tenure of U.S. President Barack Obama, who’s made inroads toward curtailing Iran’s atomic aspirations but not North Korea’s.

This latest one, in particular, “puts the U.S. on the spot,” according to Chinoy.

“Will any of their steps do anything to restrain North Korea?” the analyst mused. “My guess is probably not.”

A heavy militarized state

Combined with its secrecy and seclusion, North Korea’s us-against-the-world perspective and the fact it doesn’t play by traditional rules makes it unpredictable at best and dangerous at worst. Add nuclear weapons to the mix — even if they aren’t thermonuclear — and Pyongyang could unleash devastation of a sort not seen in over 70 years.

That’s when U.S. forces used atomic bombs on the Japanese cities of Hiroshima and Nagasaki, ending World War II. Minuscule in power compared with H-bombs, the two blasts nonetheless killed about 200,000 people.

While it’s done little outwardly to develop its economy, North Korea has put a lot of focus on its military, carrying a huge standing army of 1.2 million active soldiers plus 7.7 million reservists in a country of 25 million people.

“If a nuclear device has been detonated… it underlines the very real threat that North Korea represents to regional and international security,” British Foreign Secretary Philip Hammond said.

Expert: Hard to disprove North Korea’s claim

Its conventional weaponry is dated, with limited effectiveness. That’s one reason, experts speculate, Pyongyang has sought nuclear weapons — to project power internationally.

Last May, North Korea claimed it had the ability to miniaturize nuclear weapons, a development that would allow it to deploy nuclear weapons on missiles. A U.S. National Security Council spokesman responded at the time that the United States did not think the North Koreans had such a capability.

Still, the possibility of Pyongyang being able to strike the U.S. mainland, even now, can’t be ruled out. And there’s no doubt that South Korea and Japan — two countries that Washington has long vowed to defend — are within reach.

David Albright, a former U.N. weapons inspector, told CNN last year that Pyongyang could already have 10 to 15 atomic weapons, and that it could grow that amount by several weapons per year.

He believed then that Pyongyang had the capability to miniaturize a warhead for shorter missiles, but not yet for intercontinental ballistic missiles capable of reaching the United States.

Albright called the latest nuclear test “largely a mystery,” and surmised that North Korea didn’t test a standard two-stage hydrogen bomb, in which an atomic blast sets off a thermonuclear explosion. He said it’s possible “another thermonuclear weapon design” was tested, noting there “are many types of such weapons” that “can achieve very high explosive yields.”

“While awaiting success, North Korea can bluff,” said Albright, the founder of the Institute for Science and International Security. “It can claim that it now knows how to achieve high yields with thermonuclear concepts. It is difficult to prove it does not.”

CNN’s Jim Acosta, Jim Sciutto, Richard Roth, Tim Hume, Elise Labott, HyoungJoo Choi, Junko Ogura, Serena Dong and Shen Lu contributed to this report.