A strong earthquake shook northern Japan on Wednesday and Japanese media reported the government had detected tremors in North Korea as well, leading it to suspect Pyongyang had conducted a second nuclear test.

But Japanese Prime Minister Shinzo Abe as saying he had no information to confirm a second North Korean test had taken place and U.S. and South Korean monitors said they detected no new seismic activity Wednesday in North Korea.

CountryWatch: North Korea

"I have had not received information about any indications ... that a test has take place," Abe said at a parliamentary budget meeting.

In Washington, a Pentagon spokesman, Army Lt. Col. Brian Maka, said of the reports on North Korea: "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."

The first reports came from Japanese media which cited government officials as saying they had detected tremors in North Korea, leading them to suspect the government there had conducted a second nuclear test just two days after its first-ever such test alarmed the world and provoked global condemnation.

Abe's spokesman said the government was trying to confirm whether the North had tested another nuclear device.

About a half hour after the first media reports came out, Japan's meteorological agency said it had detected a strong magnitude-6.0 earthquake in northeastern Japan.

It was not immediately clear whether that earthquake had led to the scare about a new nuclear test.

The U.S. Geological Survey said it was still checking reports on new seismic activity in North Korea on Wednesday.

"So far, do not see any event in North Korea," said USGS official Bruce Presgrave. "There very definitely was an earthquake in Japan. We see one magnitude-5.8 at this time. There could have been other events in Japan that are smaller, we're still checking," he added.

"We've been trying to find a reported event in North Korea. There's been nothing big enough to trigger our alarms. Either the event is too small or we're not looking at the right time for it."

The head of South Korean seismic monitoring station said no activity has been detected in North Korea that could indicate a possible second North Korea nuclear test.

"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.

Click here to go to FOXNews.com's North Korea Center.