North Korea has pulled manpower and equipment from its nuclear test site, government sources said Monday, a possible sign of an imminent nuclear blast.

The South Korean government has been keeping a close watch on North Korea as no movement of manpower and equipment has been observed since Friday at the country's Punggye-ri nuclear test site, the sources said.

However, it's unclear whether the withdrawal is temporary or not, they said.

North Korea has warned of a third atomic test since last month but did not specify a date.

"When manpower and equipment are withdrawn, it can be an indication that a nuclear test is imminent," one source said, requesting that he not be identified. "We're watching the developments closely to know whether a nuclear test is imminent or it's another deceptive tactic."

Another Seoul government source said the withdrawal appears to be something to do with the Lunar New Year's holiday that North Korea celebrates for three days starting on Sunday.

Seoul officials predicted that Pyongyang may carry out its threatened third nuclear test between the end of the holiday and late leader Kim Jong-il's birth anniversary of Feb. 16.

North Korea has previously conducted nuclear tests in 2006 and 2009. (Yonhap News)