North Korea announced it conducted its fifth nuclear test on Friday, hours after seismic monitors detected a blast near the secretive country’s nuclear test site, and triggered tensions in neighbouring South Korea and Japan.
The country’s state TV said the North was now capable of mounting nuclear warheads on ballistic rockets. It also said the test, which international agencies claim is likely the North’s biggest so far, had no leakage of nuclear material and no environmental impact.
US, European and Chinese agencies reported that a tremor was recorded at 0030 GMT with a magnitude of 5.3.
The quake was detected near North Korea’s Pyunggye-ri nuclear test site as the country celebrates Foundation Day, which marks the anniversary of the founding of the nation in 1948.
South Korea’s military said it was analysing the nature of the tremor, and called an emergency meeting of its National Security Council.
“Today at around 9:30 am, we detected an artificial earthquake wave at magnitude 5.0 in the area of North Korea’s Punggye-ri and we are analysing whether it is a nuclear test,” South Korea’s joint chiefs of staff said in a statement, referring to the North’s nuclear test site.
The China Earthquake Networks Center also said the tremor was a suspected explosion. China’s environment ministry began emergency radiation monitoring along its borders with North Korea in northeast China, state television reported.
Japanese Prime Minister Shinzo Abe said such a nuclear test could not be tolerated. Japan’s foreign minister lodged a protest and Tokyo also sent two military jets to begin measuring for radiation.
Jeffrey Lewis of the California-based Middlebury Institute of International Studies said the highest estimates of seismic magnitude suggested this was the most powerful nuclear test conducted by North Korea so far.
He said the seismic magnitude and surface level indicated a blast with a 20- to 30-kilotonne yield. Such a yield would make this test, if confirmed, larger than the nuclear bomb dropped on the Japanese city of Hiroshima in World War Two and potentially bigger than that dropped on Nagasaki soon after.
“That’s the largest DPRK test to date, 20-30kt, at least. Not a happy day,” Lewis told Reuters, using the North’s official title of the Democratic People’s Republic of Korea.
“The important thing is that five tests in, they now have a lot of nuclear test experience. They aren’t a backwards state any more,” he said.
The Japan Meteorological Agency official said the seismological data was unusual and that it was now analysing the data.
“The form of the wave is different than in a normal quake,” the official said according to public broadcaster NHK.
Initial analysis of North Korea’s January test estimated a yield of just 6 kilotonnes.
South Korea’s Yonhap news agency reported that the South’s military believed the seismic event indicated a blast with a 10-kilotonne yield, still the largest ever conducted by the secretive North.
Kune Y Suh, a nuclear engineering professor at Seoul National University, said the latest test, if confirmed, appeared to be two to three times larger than earlier tests, with a potential yield of more than 10 kilotonnes.
“So North Korea can now show off their nuclear capability proudly,” Suh said.
Lassina Zerbo, the head of world monitoring agency the Comprehensive Nuclear-Test-Ban Treaty Organisation, said the seismic activity registered on Friday was larger than that triggered by the North’s test in January.
That test was recorded with a magnitude of 5.1, according to the US Geological Survey.
The White House’s National Security Council said it was aware of seismic activity on the Korean Peninsula. “We are monitoring and continuing to assess the situation in close coordination with our regional partners,” an NSC statement said.
US-based 38 North, a North Korea monitoring project, said in a note late on Thursday that satellite images showed fresh activity at North Korea’s Punggye-ri test site.
Isolated North Korea’s fourth nuclear test in January resulted in tough new UN sanctions. It has conducted a series of missile tests since then, including of a submarine-launched missile, in defiance of those resolutions.
North Korea has been hit by five sets of United Nations sanctions since it first tested a nuclear device in 2006.
It also test-fired three ballistic missiles on Monday as world powers gathered for a G20 meeting in China, with leader Kim Jong-Un hailing the tests as “perfect”, and US President Barack Obama warning it would only up the pressure.
A nuclear test is another slap in the face to the North’s chief ally China and diminishes any chance of a resumption of six-country talks on North Korea’s nuclear programme.
After a previous nuclear test in 2013, the North restarted a plutonium reactor that it had shut down at its Yongbyon complex in 2007 under an aid-for-disarmament accord.