The United States detected no seismic activity indicating a second nuclear test by the Democratic People's Republic of Korea, a Pentagon spokesman said Tuesday.

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

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

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.

South Korea and Japan also denied any seismic activity had been detected in the DPRK to confirm a second test.

A spokesman for the South Korean presidential office said, "So far we have not received reports of fresh seismic activity."

Japan's meteorological agency said Wednesday that it had not detected any seismic activity.

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

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