SEOUL: The United States, South Korea and Japan agreed to launch a “united and strong” international response to North Korea’s claim of a successful hydrogen bomb test, as experts scrambled Thursday to find more details about the detonation that drew worldwide skepticism and condemnation.
It may take weeks or longer to confirm or contradict the North’s claim, but a successful test would mark a major and unanticipated advance for its still-limited nuclear arsenal and push its scientists and engineers closer to their goal of building a warhead small enough to place on a missile that can reach the U.S. mainland.
Separate statements from the White House said President Barack Obama had spoken to South Korean President Park Geun-Hye and to Prime Minister Shinzo Abe of Japan. The statements said the countries “agreed to work together to forge a united and strong international response to North Korea’s latest reckless behavior.”
Obama also reaffirmed the “unshakeable U.S. commitment” to the security of South Korea and Japan, according to the statements.
The North’s bomb test drew immediate worldwide condemnation, with the U.N. Security Council holding an emergency session and pledging to swiftly pursue new sanctions against North Korea, saying its test was a ‘clear violation’ of previous U.N. resolutions.
Four rounds of U.N. sanctions have aimed at reining in the North’s nuclear and missile development programs, but Pyongyang has ignored them and moved ahead with programs to modernize its ballistic missiles and nuclear weapons.
South Korean officials said they were considering a variety of punitive measures. The options include restarting border propaganda broadcasts that Seoul halted after it agreed with Pyongyang in late August on a package of measures aimed at easing animosities, Defense Minister Han Min-koo told lawmakers Thursday.
On Wednesday, there was a burst of jubilation and pride in North Korea’s capital of Pyongyang, where a TV anchor said the test of a “miniaturized” hydrogen bomb had been a “perfect success” that elevated the country’s “nuclear might to the next level.”
But an early analysis by the U.S. government was “not consistent with the claims that the regime has made of a successful hydrogen bomb test,” White House spokesman Josh Earnest said.
He added that nothing had happened in the last 24 hours to change Washington’s assessment of Pyongyang’s technical or military capabilities.
South Korea’s spy agency told lawmakers that it thought the estimated explosive yield from the blast was much smaller than what even a failed hydrogen bomb detonation would produce.
Other analysts agreed with that assessment.
“I’m pretty skeptical,” said Melissa Hanham, senior researcher at the James Martin Center for Nonproliferation Studies at the Middlebury Institute for International Studies in Monterey, California. “The seismic data indicates it would be very small for a hydrogen test.
While also noting the quake was likely too small for an H-bomb test, Jaiki Lee, a professor of nuclear engineering at Seoul’s Hanyang University, said the North could have experimented with a “boosted” hybrid bomb that uses some nuclear fusion fuel along with more conventional uranium or plutonium fuel.
Fusion is the main principle behind the hydrogen bomb, which can be hundreds of times more powerful than atomic bombs that use fission. In a hydrogen bomb, a nuclear fission explosion sets off a fusion reaction responsible for a powerful blast and radioactivity.
Washington and nuclear experts have been skeptical of past North Korean claims about hydrogen bombs, which are much more powerful and much more difficult to make than atomic bombs.
North Korea’s state media called the test a self-defense measure against a potential U.S. attack. “The (country’s) access to H-bomb of justice, standing against the U.S., the chieftain of aggression is the legitimate right of a sovereign state for self-defense and a very just step no one can slander.”
The hydrogen bomb already is the global standard for the five nations with the greatest nuclear capabilities: the U.S., Russia, France, the U.K. and China. Other nations may also either have it or are working on it, despite a worldwide effort to contain such proliferation.