North Korea is suspected of conducting a third nuclear test on Tuesday, said South Korea’s defense ministry, after seismic activity was detected by the U.S. Geological Survey.
The tremor was a 4.9-magnitude, shallow quake.
The epicenter of the seismic activity was near North Korea’s known nuclear test site.
An international nuclear test monitoring agency said the location of the seismic activity was “roughly congruent with” 2006 and 2008 tests carried out by the North Koreans and had “clear explosion-like characteristics”.
On Monday, North Korea had informed Beijing and Washington of its plans to conduct such a test.
North Korea is not generally known for its seismic activity, and it may take days to ascertain whether a nuclear test was performed.