An earthquake was detected Tuesday in North Korea just north of a site where the country has conducted nuclear tests.

Neither Pyongyang nor Seoul confirmed whether the tremor resulted from a widely anticipated third nuclear test, though an analyst in Seoul said a nuclear detonation was a ``high possibility.''

The South Korean Defence 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.

A U.N. nuclear test monitoring organization detected what it called an ``unusual seismic event'' in North Korea.

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.