NEW YORK // Doubts have been cast on North Korea’s claim that it exploded a hydrogen bomb early on Wednesday at a nuclear test site in the country’s north east.
Experts said the blast was too small to have been a thermonuclear fusion bomb, “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 specialist Crispin Rovere.
Bruce Bennett, a senior defence analyst with the Rand Corporation, said if a hydrogen bomb was actually tested, it failed. “If it were a real H-bomb, the Richter scale reading should have been about a hundred times more powerful.” said Mr Bennett.
Despite the scepticism, last night the UN security council – including China, Pyongyang’s ally – “strongly condemned” the test, said it was a “clear threat to international peace and security” and began work on preparing further sanctions against North Korea.
The test also drew widespread condemnation from the international community.
South Korean president Park Geun-hye condemned the “grave provocation” and called for a strong international response.
The UN secretary general Ban Ki-moon said he “unequivocally” condemned the test and demanded that North Korea “cease any further nuclear activities”.
The United States said it was studying the precise nature of the test and would “respond appropriately”.
Beijing has restrained US-led allies from stronger action against Pyongyang in the past, but has shown increasing frustration with the North’s refusal to suspend testing.
In an initial reaction, the foreign ministry in Beijing said it “firmly opposes” the nuclear test, which was carried out “irrespective of the international community’s opposition”.
Three previous tests in 2006, 2009 and 2013 triggered waves of UN sanctions.
The new test, just two days before the North Korean leader Kim Jong-un’s birthday, was initially detected as a 5.1-magnitude tremor at the North’s main Punggye-ri nuclear test site in the northeast of the country.
North Korean state television said “the republic’s first hydrogen bomb test” had been “successfully performed at 10am [0130 GMT]”.
“We have now joined the rank of advanced nuclear states,” it said.
State television showed Mr Kim’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”.
The weapons yield was initially estimated at between six and nine kilotons – similar to the North’s last nuclear test in 2013.
A hydrogen 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, Mr Kim suggested Pyongyang had already developed such a device.
That claim was questioned by international experts at the time, and there was continued scepticism yesterday.
“The device is highly unlikely to have been a hydrogen bomb, as announced by North Korean media outlets, but is possibly a ‘boosted fission weapon’, indicative of North Korea’s developing weapons capabilities. It’s highly likely that the claim of a hydrogen bomb is disinformation by the North Korean regime,” according to a risk analysis report by IHS Jane’s.
South Korea’s defence ministry also said it doubted the explosion was thermonuclear.
Most experts had assumed Pyongyang was years from developing a hydrogen bomb, while assessments were divided on how far it had gone in developing a miniaturised warhead to fit on a ballistic missile.
Wednesday’s test was a striking act of defiance in the face of warnings from enemies and allies alike that Pyongyang would pay a steep price for moving forward with its nuclear weapons programme. The final response of China, North Korea’s economic and diplomatic patron, will be key in determining the international community’s next step.
“Beijing will face increased pressure both domestically and internationally to punish and rein in Kim Jong-un,” said Yanmei Xie, the International Crisis Group’s senior analyst for Northeast Asia.
But China’s leverage over Pyongyang is restricted by its overriding fear of a North Korean collapse.
“A nuclear-armed North Korea is uncomfortable and disturbing,” Mr Xie said.
“But a regime collapse in Pyongyang leading to mass chaos next door and potentially a united Korean peninsula with Washington extending its influence northward to China’s doorstep is downright frightening.”
* Agence France-Presse, with additional reporting from Reuters