North Korea's triumphal declaration that it detonated its first hydrogen bomb drew global condemnation and threats of new sanctions against the isolated nuclear power Wednesday. But it also raised skepticism from the White House and defence experts, who questioned Pyongyang's claim to a new and vastly more destructive weapon.
Hours after seismic sensors detected an artificial earthquake that sent schoolchildren in nearby China running for safety, a smiling North Korean television announcer said the country had "become a nuclear state which also holds a hydrogen bomb."
UN Secretary-General Ban Ki-moon called the test "profoundly destabilizing for regional security," and a hastily called United Nations Security Council meeting agreed to consider "further significant measures" against North Korea. Sanctions set in place after a 2006 nuclear test, North Korea's first of four, already banned sales of arms and luxury goods to the country. Stronger economic and commercial sanctions were set in place following subsequent tests.
North Korea must pay "the commensurate price for the latest nuclear test," South Korean President Park Geun-hye said, joining a chorus of rebukes from China, Russia, Japan, Australia and the United Kingdom. Foreign Affairs Minister Stéphane Dion said Ottawa "condemns without reservation the reckless behaviour" of Pyongyang.
Under Kim Jong-un, the isolated state has spurned international demands to lay down its nuclear arms, pursuing instead aggressive new advances in weapons technology. It has launched a long-range rocket – a potential first step toward building a globe-spanning intercontinental missile – test-fired missiles from submarines and sought to miniaturize nuclear weapons to serve as warheads that can rain down on distant targets.
Yet it's not clear how much the weapons program has accomplished. Rocket launches and submarine missile tests have been marred with failures. And the Wednesday blast of what North Korea called its "H-bomb of justice" appeared to be less powerful than North Korea's 2013 detonation of a plutonium-based atomic bomb, raising doubts that it has engineered a massively more sophisticated and destructive weapon.
"The initial analysis is not consistent with the North Korean claims of a successful hydrogen bomb test," said White House spokesman Josh Earnest.
The country does not appear to have the ability to manufacture lithium deuteride, an important hydrogen bomb ingredient, making it "quite likely that claims of a hydrogen bomb are disinformation by the North Korean regime," said Karl Dewey, an expert on nuclear proliferation with defence publication IHS Jane's.
More likely, he said, is that the country tested a "boosted fission weapon," a hybrid that adds hydrogen isotopes to a standard plutonium bomb, "greatly enhancing the original explosion by factors of five or more," Mr. Dewey said.
Such a device would be far less deadly than a hydrogen bomb, but still mark a major advance for North Korea, whose state media also said it had succeeded in shrinking the weapon's size.
The test suggested North Korea's Mr. Kim is "serious" about pursuing more deadly armaments and not merely posturing, said Joel Wit, a former U.S. State Department official who is a senior fellow at the U.S.-Korea Institute at Johns Hopkins University.
Mr. Wit called for the international community to rethink its approach to a country that has laughed off global opposition to its nuclear program.
"Our policies aren't working and we all need to go back to the drawing board, figure out what could be more effective," he said.
The failure of other nations to force Pyongyang to abandon its nuclear-weapons program is made more glaring by the recent U.S.-led deal with Iran intended to keep that nation from developing nuclear weaponry.
But the success of any measure will depend largely on China, which has long offered enough support to Pyongyang to keep its regime from a collapse that would bring trouble across the long, shared border. Some 60 per cent of North Korean trade is with China, which supplies the country with food, arms and energy.
The claims of a hydrogen bomb have underscored for China "that the North Korea nuclear issue has become very severe now," said Zhang Liangui, a professor of international strategic research at the Communist Party's Central Party School, who argued for a more muscular response.
"The international community should take clearer, firmer and more effective policies and measures for the denuclearization of the Korean Peninsula," he said.
But Chinese officials would not commit to further measures beyond verbal condemnation.
Asked whether Beijing would consider stricter sanctions, foreign ministry spokeswoman Hua Chunying on Wednesday said "China will honour its international obligations."
She said China was not warned about the test and called for the urgent resumption of six-party talks – between the two Koreas, the United States, Russia, China and Japan, which have not been held since 2007 – and denuclearization of the Korean peninsula. "Our position is clear: We oppose their test," Ms. Hua said.
But even more extreme international pressure is unlikely to dissuade Pyongyang from pursuing further nuclear arms, said Andrei Lankov, a professor of Korean Studies at Kookmin University in Seoul who is an expert on North Korea.
"They are a nuclear power and they will remain a nuclear power," he said. "They believe that they will put themselves actually at great risk if they choose to denuclearize. Probably they are right."
In an statement, North Korea said it was a "responsible nuclear-weapons state" that would not employ a first strike, and that it needed nuclear arms to stand "against the U.S., the chieftain of aggression."
With a report from Yu Mei