Military sources say that "consistent movements" have been detected in Kilju County in North Korea's North Hamgyeong Province, possible signs of a second nuclear test.

Kilju is the presumed site of the North's first test earlier this month.

A source says that South Korean military and intelligence are trying to determine if the apparent construction of an unidentified building relates to a second nuclear test.

It said they have yet to ascertain if the movement of trucks and activities of North Korean soldiers indicate preparations for another test, or is simply a staged act by Pyongyang.

Another military source says that movements have certainly been detected in the area but does not see a second test impending.