The suspected North Korean nuclear test appears to be “pretty similar” to Pyongyang’s last test in 2013, according to the head of the international agency tasked with monitoring such incidents.
This initial finding adds to scepticism about the North Korean claim that it has tested a much more powerful hydrogen bomb – a development that, if true, would mark significant progress in its nuclear capability.
The announcement on North Korean TV that a “miniaturised hydrogen bomb” was successfully tested underground on Wednesday morning provoked outrage from the US, China, Japan, South Korea, the United Nations and Nato.
The 2013 test was estimated to have involved an atomic fission device with a yield of between six and nine kilotons, smaller than the bombs dropped on Hiroshima and Nagasaki. Hydrogen – or thermonuclear – weapons use a primary fission blast to set off a much bigger blast caused by fusion. The yield is typically more than a thousand times greater.
Nuclear experts said that North Korea could be experimenting with a hybrid – a boosted fission device, in which small amounts of hydrogen isotopes deuterium and tritium are placed inside the core of an atomic bomb to increase its yield through fusion. But if that had been successful it should have produced a yield in the tens of kilotons range.
The seismic shock from the new suspected test – the country’s fourth nuclear test if confirmed – was detected and reported by the preparatory commission for the Comprehensive Test-Ban Treaty Organisation, based in Vienna, which monitors suspected tests while seeking to rally international support to bring the test ban into force.
“We have about 30 stations who have seen the event through this point in time. That was a couple of hours after the event. Our analysts are working hard to try to give the best estimates and fine-tune the data in order for us to have the best technical specification of this event,” Lassina Zerbo, the commission’s executive secretary, told the Guardian.
Zerbo said that the initial seismic readings suggested a similar test to the one carried out by North Korea three years ago. “It is close to what happened in 2013. I think they are pretty similar in terms of location, magnitude and so forth.”
He added that confirmation of a nuclear test would only come once winds had driven particles released in the blast towards CTBTO monitoring stations in countries neighbouring North Korea. “To confirm if an event is nuclear we need the smoking gun, which is the radio isotopes that are released from a blast,” Zerbo said. “We have a network of stations and the winds will blow the venting to our stations. We have some stations in Japan, in Russia and in the vicinity and those stations may be able to pick up something in the next 48 or 72 hours.”
It will not in the CTBTO commission’s mandate to determine what kind of weapon has been tested, but scientists should be able to determine whether a hydrogen bomb was involved on the basis of which radionuclides are picked up. In 2013, it took 50 days for such particles to be detected but analysts are hopeful confirmation of this blast will come earlier as the US Geological Survey estimated that the suspected test was close to the surface.
Zerbo said the best way for the international community to put pressure on North Korea or any other states contemplating new nuclear tests, is for countries who have so far not ratified the comprehensive test-ban treaty to join. Twenty years after the treaty was adopted by the UN, there are still eight key states who need to join for it to become legally binding. Five of those – the US, Iran, Israel, Egypt and China – have signed but not ratified it. Another three – North Korea, India and Pakistan – have not even signed it.
“These eight countries should show leadership to ensure this doesn’t happen again,” Zerbo said. “We need people to work on this issue. We don’t want to see more tests before people think this treaty is important. The only way to stop this is to make it legally binding. I hope this will be the last wake-up call to the international community to act on this treaty.”
The North Korean state television broadcast said the test was a “complete success” and that it had propelled the country into the “rank of advanced nuclear states”. It had been overseen by the country’s leader, Kim Jong-un, and conducted ahead of his 33rd birthday this Friday.
“[North Korea’s] fate must not be protected by any forces, only by [North Korea] itself,” the broadcast said. North Korea would not abandon its nuclear weapons program as long as the US maintained what it called “its stance of aggression”.
“The US has gathered forces hostile to DPRK [Democratic People’s Republic of Korea] and raised a slanderous human rights issue to hinder DPRK’s improvement,” it said. “It is just to have H-bomb as self-defence against the US having numerous and humongous nuclear weapons. The DPRK’s fate must not be protected by any forces but DPRK itself.”
North Korea conducted nuclear tests in 2006, 2009 and 2013, drawing condemnation and rounds of UN sanctions banning trade and financing activities that aid its weapons programme. A successful fourth test could deepen North Korea’s international isolation if the UN security council decided to respond with more sanctions. Pyongyang is thought to have developed several crude nuclear weapons.
The test is bound to ratchet up tensions between the isolated country and its neighbours as well as Washington. China’s foreign ministry said that Beijing did not have advance knowledge of the test and added that it firmly opposed Pyongyang’s action.
The South Korean president, Park Geun-hye, said the country would take decisive measures against any additional provocations by North Korea and work with the international community to make sure the country pays the price for its latest nuclear test.
Japan’s prime minister, Shinzo Abe, said his country would make a firm response to North Korea’s challenge against nuclear non-proliferation, calling its test a threat to Japan’s security.
The UN security council was planning to meet on Wednesday in New York to discuss North Korea’s nuclear test, council diplomats said. The White House said it could not confirm North Korea’s claims, but added the US would respond appropriately to provocations and defend its allies. The EU said the test was a “grave violation” of UN resolutions.
Philip Hammond, the British foreign secretary, said during a visit to Beijing: “I think I can say that Britain and China are pretty much completely aligned on North Korean nuclear. We both strongly oppose the acquisition or testing of nuclear weapons by North Korea and we both want to see a resumption of the six-party talks.”
Since becoming North Korean leader in late 2011, Kim has stepped up condemnation of joint US-South Korean military drills he believes are preparation for an invasion. In early 2013, Kim responded to UN sanctions imposed after North Korea’s third nuclear test by unleashing a barrage of threats aimed at South Korea, the US and Japan.
Kim appears to have caught the world off-guard yet again. He did not mention his country’s pursuit of a nuclear deterrent in his new year address, an omission some analysts said was designed to improve the prospects of a summit with the Chinese leader, Xi Jinping.
Speculation that the regime in Pyongyang had conducted a surprise nuclear test on Wednesday arose after seismologists from South Korea, China and other countries said they had detected a “manmade” earthquake in the country that could have been caused by an explosion.
The US last month dismissed Kim’s claims that his country had developed a hydrogen bomb.