More signs of imminent nuclear test detected in N. Korea

Increased activity has been spotted at a tunnel of North Korea's main underground nuclear site, a South Korean government source said Saturday, the latest indication the communist state is preparing to conduct a third test.

"At a tunnel in the southern part of the test site in Punggye-ri, we've found that work presumed to be part of preparations for a nuclear test has entered its final stage," said a government source in Seoul on condition of anonymity.

It is the latest in a recent series of signs that the North may be preparing for another nuclear test.

The communist country has threatened to detonate a nuclear device in retaliation for the U.N. Security Council's resolution condemning its Dec. 12 long-range rocket launch. On Friday, sources here said the North has put a screen over the entrance to the test site's western tunnel in what was seen as an attempt to thwart outside monitoring of the detonation.