South Korean and US seismic monitoring stations said early Wednesday they hadn't detected any activity that could indicate a possible second North Korea nuclear test, responding to media reports of a possible explosion.
"There's no signal from North Korea, even no small event," Chi Heon-cheol, director of the South's Korea Earthquake Research Center, told The Associated Press.
"There has been no activity in the last two hours," US Geological Survey official Rafael Abreu told AP just after 9 a.m. (0000 GMT) in Korea.
The agency can detect most tremors if they are above 3.5 magnitude, he said.
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