The United States said yesterday that it can't confirm a report by Japanese national broadcaster NHK that the Democratic People's Republic of Korea has conducted a second nuclear test.

"We have no confirmation of a second test," White House spokesman Blair Jones told Xinhua.

"We will continue to monitor the situation closely, together with allies," he added.

Earlier, Lieutenant Colonel Brian Maka, spokesman for the Pentagon, said the U.S. detected no seismic activity indicating a second nuclear test by the DPRK

"We have no credible evidence" of a second test "and no seismic activity has been detected," said Maka.

The US Geological Survey also said it was still checking reports on new seismic activity in DPRK 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."