SEOUL—North Korea said Wednesday it had carried out a “successful” miniaturized hydrogen bomb test—a shock announcement that, if confirmed, would massively raise the stakes in the hermit state’s bid to strengthen its nuclear arsenal.
The announcement triggered swift international condemnation but also skepticism, with experts suggesting the apparent yield was far too low for a thermonuclear device that the North was believed to be years from developing.
“The republic’s first hydrogen bomb test has been successfully performed at 10:00 am (0130 GMT),” North Korean state television announced.
“With the perfect success of our historic H-bomb, we have joined the rank of advanced nuclear states,” it said, adding that the test was of a miniaturized device.
The television showed North Korean leader Kim Jong-Un’s signed order—dated December 15—to go ahead with the test, with a handwritten exhortation to begin 2016 with the “thrilling sound of the first hydrogen bomb explosion”.
South Korean President Park Geun-Hye condemned the test as a “grave provocation” and called for a strong international response as the UN Security Council called an emergency meeting.
The White House said it was still studying the precise nature of the apparent test and vowed to “respond appropriately”.
A hydrogen, or thermonuclear, bomb uses fusion in a chain reaction that results in a far more powerful explosion than the fission blast generated by uranium or plutonium alone.
Last month Kim suggested Pyongyang had already developed such a device.
The claim was questioned by international experts at the time and there was continued skepticism over Wednesday’s test announcement, which took the entire international community by surprise.
“The seismic data that’s been received indicates that the explosion is probably significantly below what one would expect from an H-bomb test,” said Australian nuclear policy and arms control specialist Crispin Rovere.
The test, which came just two days before Kim Jong-Un’s birthday, was initially detected by international seismology centers as a 5.1-magnitude tremor next to the North’s main Punggye-ri nuclear test site in the northeast of the country.
Bruce Bennett, a senior defense analyst with the Rand Corporation, said if it was an H-bomb that was tested, then the detonation clearly failed—at least the fusion stage.
“If it were a real H-bomb, the Richter scale reading should have been about a hundred times more powerful,” Bennett told AFP.
Most experts had assumed Pyongyang was years from developing a thermonuclear bomb, while assessments were divided on how far it had gone in developing a miniaturized warhead to fit on a ballistic missile.
Whatever the nature of the device, it was North Korea’s fourth nuclear test and marked a striking act of defiance that flew in the face of enemies and allies alike, who have warned Pyongyang it would pay a steep price for moving forward with its nuclear weapons program.
The three previous tests in 2006, 2009 and 2013 triggered waves of UN sanctions. Their failure to prevent a fourth detonation will put the Security Council under intense pressure to take more drastic action this time around.