South Korean and U.S. 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," U.S. 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.
In Tokyo, a Japanese Foreign Ministry official said earlier Wednesday that the Japanese government suspected that North Korea conducted a second nuclear test. The official, speaking on condition of anonymity, declined to give details.
In Washington, a Pentagon spokesman, Army Lt. Col. Brian Maka, said: "We have received no credible information to confirm any of that. No seismic activity has been detected on our part."
White House spokesman Blair Jones said, "We have no independent confirmation of the second test."
