The U.S. Geological Survey is reporting a 4.9 magnitude earthquake in North Korea, raising fears that Pyongyang may have gone ahead with its threat to conduct a third nuclear test.
The USGS report put the epicenter of the quake in Kilju county, near where North Korea's Punggye-ri nuclear test site is located. It said the depth of the tremor was very shallow, at just one kilometer.
South Korean officials would not confirm whether the widely anticipated nuclear test had taken place, but several officials says it is the "likely" cause of the quake. North Korea is not prone to seismic activity.
South Korean President Lee Myung-bak has convened a meeting of the National Security Council in response to the suspected test.
VOA correspondent Steve Herman in Tokyo says that Seoul's Defense Ministry has raised its military alert status, and is watching for additional explosions or missile launches.
"There's also concern that North Korea, at the same time that it was doing this nuclear test, or on the same day, might also launch some medium-range missiles, (but) we've had no confirmation of any such activity so far." Herman said. "This is being taken very seriously by North Korea's neighbors, especially South Korea and Japan."
United Nations diplomats say an emergency session of the Security Council will be held early Tuesday in New York.
North Korea had threatened to carry out its third nuclear test in retaliation for United Nations sanctions that were expanded last month in response to a recent long-range rocket launch.
North Korea is banned from conducting nuclear and missile tests under U.N. sanctions passed in 2006 and 2009.
Earlier Tuesday, North Korean state media threatened an unspecified "high-intensity" action, but did not mention any possible nuclear test. Last month, Pyongyang threatened to continue nuclear and missile tests it said were aimed at the United States.
Since then, there had been much speculation about the timing of the possible test. South Korean officials told various media outlets that North Korea informed the U.S. and China of the impending test.
China, North Korea's only major ally and an important source of economic aid, agreed to the Security Council sanctions last month, and has expressed unusual criticism of North Korea's nuclear program.
There was no immediate word from North Korea about the seismic activity.
The Comprehensive Nuclear Test Ban Treaty, an international monitoring group, said in a statement that further analysis is needed to determine whether a nuclear test caused the the earthquake, which it said exhibited "explosion-like" characteristics.
If confirmed as a nuclear test, the organization said the act "would constitute a a clear threat to international peace and security."
This story first appeared on Voice of America & is reposted here with permission.
NOTE: The “N. Korea vows 'high-intensity' action, new rocket launches” Link in the above was added by PacificSentinel for clarity & context.
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