"So far we have not received reports of fresh seismic activity," a presidential spokesman said.

The Japanese broadcaster NHK reported earlier that "tremors" had been detected, prompting the investigation in a possible second nuclear test.

A spokeswoman at the Japanese prime minister office also denied the report, saying that "We have had no information on the report yet."

Frederick Jones, spokesman for the White House's National Security Council, said that the United States had "no confirmation" of a possible second nuclear test by the DPRK.

A Pentagon spokesman also said that the United States had detected no seismic activity indicating the reported second test.

The DPRK announced on Monday that it had conducted a successful underground nuclear test.