Seismic activity has been detected in North Korea, several nations say, in what could be a sign of a widely anticipated nuclear test.
The US Geological Survey said it had detected a tremor with a 4.9 magnitude.
South Korean media also reported a “man-made earthquake” in its northern neighbour.
North Korea said last month it was planning to carry out its third nuclear test – despite a threat from the UN Security Council of “consequences”.
The USGS said the quake occurred at a depth of 1km. It put the epicentre close to North Korea’s known nuclear test site in the northeast of the country.
China’s Earthquake Administration described it as a “suspected explosion”, AFP reported. Japan’s Meteorological Agency said the tremor was “different from a normal earthquake”.
“We believe that there is a possibility that North Korea carried out a nuclear test, looking at past cases,” said Chief Cabinet Secretary Yoshihide Suga.
Yonhap news agency says South Korea has raised its military alert in response to the quake. Japan says it will hold a meeting of its national security council, public broadcaster NHK reported.
North Korea is not prone to seismic activity. It conducted nuclear tests in 2006 and 2009, each time after rocket launches condemned by the UN as disguised tests of long-range missile technology.
It announced in January that it planned to conduct a “high-level” nuclear test, in response to expanded UN sanctions imposed after its latest rocket launch on 12 December 2012.
There has been no word yet from North Korea on what has taken place. (BBC)