Surveillance of North Korea's atomic test site shows a heightened level of movement by vehicles and personnel, further lending credence to the view that a third nuclear detonation is imminent, the Yonhap News Agency reported on Wednesday.
"There was increased activity by workers and vehicles near the entrance tunnel at the Punggye-ri test site," an anonymous South Korean government insider said. "It seems that the activities are aimed at preparing for a nuclear test at any moment."
Pyongyang in the last week has made multiple threats of carrying out another nuclear test after being hit with toughened U.N. Security Council sanctions for the North's launch last month of a long-range rocket.
It difficult to determine precisely when the detonation could take place, according to the source.
Pyongyang could time its test either to the Feb. 16 birthday of deceased ruler Kim Jong Il or the Feb. 25 installation into office of South Korean President-elect Park Geun-hye , Yonhap separately reported, citing South Korean legislator Park Jie-won.
"North Korea has usually carried out what it repeatedly threatens to do, so I think it will conduct a nuclear test for sure," he said during a radio interview.
A number of officials and analysts believe the expected test will be powered by highly enriched uranium rather than the plutonium used by North Korea in its 2006 and 2009 detonations, the Korea Herald reported.