Chung Hyung-Keun, who served as a deputy chief of the National Intelligence Service in the 1990s, said unusual personnel and construction activity had recently been detected at Punggye in the northeast where the first nuclear test was staged on October 9.

But Chung, in an article posted on his website, said the communist state is unlikely to go ahead until it knows the outcome of an expected new round of six-nation talks on its nuclear program, and of scheduled negotiations with the United States on financial sanctions.

Chung quoted a government source as saying an unidentified object and up to 15 people were spotted at the west side of a tunnel at Punggye that was used for the first test.

"Chances are very high that the North Korean workers moved the facilities into the tunnel to prepare for an additional nuclear test," the opposition Grand National Party legislator told Yonhap news agency.

A South Korean foreign ministry official said Friday that activity has been detected near the site of the first test but there are no signs yet of preparations for a second test.

The official was speaking after US television network ABC reported that North Korea appears to have prepared for a repeat test.

The latest round of six-nation talks on the North's nuclear programme ended in Beijing in December without a breakthrough. The State Department said Friday the talks could resume as early as this month.

Financial officials from North Korea and the US are also scheduled to meet later this month to try to resolve a row over US financial sanctions imposed over the North's alleged counterfeiting and other illegal activities.