Kim Jong Un has been ratcheting up tensions with outside world since he ordered the nuclear test.
North Korea appears to have conducted its fifth nuclear test, analysts say, after a 5.0 magnitude artificial earthquake was detected near its nuclear test site Friday morning.
The test came as North Korea celebrates the "day of the foundation of the republic," the 68th anniversary of the formation of the communist regime by Kim Il Sung, the current leader's grandfather.
The United States Geological Survey reported a 5.3 magnitude earthquake near Punggye-ri, the site of North Korea's previous nuclear tests, at exactly 9 a.m. local time.
"Possible explosion, located near the location where North Korea has detonated nuclear explosions in the past," the USGS said on its website. "If this is indeed an explosion, the USGS National Earthquake Information Center cannot determine what type of explosion it may be, whether nuclear or any other possible type."
South Korea's national security council convened an emergency meeting, and Japan said it was highly likely that the explosion was a nuclear test.
In Washington, U.S. National Security Council spokesman Ned Price said in a statement: "We are aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site. We are monitoring and continuing to assess the situation in close coordination with our regional partners."
Analysts were convinced it was a nuclear test.
Jeffrey Lewis, director of the East Asia nonproliferation program at the James Martin Center for Nonproliferation Studies in Monterey, California, said it appeared to be the biggest of North Korea's five tests.
"This is clearly a nuclear test," Lewis said. "USGS is calling it an explosion because it has all the hallmarks: the waveform is sudden unlike an earthquake, the depth is shallow, the location is the North Korean test site and it happened on the half hour."
Just before the earthquake was detected, North Korea analysts at 38 North website said that satellite imagery showed movement around the underground test site, with mining carts visible and a new building erected near one portal. "Overall, this activity indicates that maintenance and minor excavation operations have resumed at Punggye-ri," Joseph S. Bermudez and Jack Liu wrote in the note. "However, it is unclear if this activity is directly related to preparations for a fifth nuclear test."
Kim Jong Un, the third generation leader of North Korea, has been ratcheting up the tensions with the outside world since he ordered the country's fourth nuclear test - which he claimed was of a hydrogen bomb - in January. This was swiftly followed by a long-range ballistic missile test.
Despite widespread international condemnation, Kim has become increasingly defiant, testing a range of missiles and apparently making some technological progress.
In its most recent salvo, North Korea launched three medium-range missiles Monday as China, which had joined the international condemnation of last month's submarine-launched ballistic missile, was hosting the G-20 meeting in Huangzhou.
The rockets flew 620 miles - putting Huangzhou within range. But they were sent in the other direction, falling inside Japan's air defense identification zone.
Last month North Korea successfully launched a missile from a submarine near its east coast port of Sinpo. It flew about 300 miles toward Japan before falling into the sea.
© 2016 The Washington Post
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