North Korea has pulled manpower and equipment out of its nuclear test site, a report said Monday, which cited the move as a possible sign of an imminent blast.
South Korea's Yonhap news agency said that Seoul has been keeping close watch on the underground Punggye-ri nuclear test site, as no movement of manpower and equipment has been observed there since Friday.
The agency quoted an unnamed source as saying the apparent withdrawal could point to a nuclear test being carried out soon.
North Korea has warned of a third atomic test since last month, but has not specified a date.
"When manpower and equipment are withdrawn, it can be an indication that a nuclear test is imminent," the source told Yonhap, requesting anonymity.
"We're watching the developments closely to know whether a nuclear test is imminent or it's another deceptive tactic," the source added.
Another Seoul government source told Yonhap that the withdrawal of manpower and equipment could be linked to the Lunar New Year's holiday, which is celebrated for three days in North Korea, having started on Sunday.
Yonhap said it was unclear whether the withdrawal was temporary.
Seoul has predicted Pyongyang may carry out its third nuclear test between the end of the holiday and the late leader Kim Jong-il's birthday on February 16, Yonhap said.
The withdrawal from the northeastern nuclear site comes after North Korea accused the United States and South Korea of "fussing over speculation" in Japan-based pro-North weekly magazine Tongil Sinbo, funded by Pyongyang.
"They are fussing over speculation without having a clue about what important state measures will be taken, including whether it will be a nuclear test or something worse than that," said the editorial, dated Friday and posted on the North's official website, Uriminzokkiri.
The North's top body, the National Defence Commission, announced on January 24 it would carry out a "high-level nuclear test" and further rocket launches, in a defiant response to tightened UN sanctions after its successful long-range rocket launch in December.
The isolated communist state insists the rocket launch was a scientific mission aimed at putting a satellite into an orbit.
But the US and many other countries viewed it as a disguised ballistic missile test, banned under UN resolutions which were triggered by Pyongyang's previous nuclear and missile tests in 2006 and 2009.
Experts and Seoul officials, citing recent satellite imagery, say the impoverished but nuclear-armed state has completed preparations for another atomic test at the northeastern nuclear site.