The North Korean military has informed China that it plans to conduct a series of underground nuclear tests, NBC News reported on Tuesday, citing unnamed US officials.
A US intelligence official speaking on condition of anonymity earlier told AFP that North Korea could conduct a test "with little or no warning," but a decision to do so would be "as much political as it is technical."
Activity detected at potential North Korean test sites may mean a second nuclear test is being prepared but not necessarily evidence that the test is imminent, the official said.
International pressure mounted early on Wednesday on North Korea not to conduct a second nuclear test after Pyongyang said UN sanctions imposed after its first test on October 9 were tantamount to a "declaration of war."