The US military has observed activity in North Korea that suggests Pyongyang may be gearing up for another nuclear test, a US official said Thursday.
"At the sites where we watch tests, we see a level of activity that's similar to what they've done before other tests," the defense official told AFP on condition of anonymity.
Fox News reported earlier on Thursday that North Korea is in the final stages of readying for another nuclear test, possibly within the coming days.
North Korea may have dug new tunnels around the Punggye-ri test site in the northeast of the country, Fox said, citing a US official.
It also reported that the US Air Force has deployed a special surveillance plane used to take air samples after nuclear tests.
North Korea is on a quest to develop a long-range missile capable of hitting the US mainland with a nuclear warhead, and staged two nuclear tests and multiple missile launches last year.