SEOUL, South Korea -- South Korea said it suspects a nuclear test caused an earthquake Tuesday in North Korea just north of a site where the country conducted two previous atomic tests.
North Korea didn't immediately confirm whether the tremor resulted from a widely anticipated third nuclear test, though an analyst in Seoul said a nuclear detonation was a "high possibility."
A U.N. nuclear test monitoring organization detected what it called an "unusual seismic event" in North Korea.
The South Korean Defense Ministry, which raised its military alert level after the quake, said it was trying to determine whether it was a test. Nuclear blasts can create tremors but they are distinct from those caused by natural earthquakes.
Kim Min-seok, a South Korean Defense Ministry spokesman, also told reporters that North Korea informed China and the United States of its plans to conduct a nuclear test. It was not clear when Pyongyang told Beijing and Washington.
The U.S. Geological Survey as well as earthquake monitoring stations in South Korea detected an earthquake just north of a site where North Korea conducted its second nuclear test in 2009, according to the government-funded Korea Institute of Geoscience and Mineral Resources.
"There is a high possibility that North Korea has conducted a nuclear test," said Chi Heoncheol, an earthquake specialist at the institute. Chi said a magnitude 3.9 magnitude earthquake and a magnitude 4.5 earthquake were detected in the North's 2006 and 2009 nuclear tests.