Seoul: North Korea is restoring facilities at its Yongbyon nuclear reactor, the source of weapons-grade plutonium in the past, South Korea`s Defence Ministry said on Tuesday.
"North Korea is restoring nuclear facilities and continuing maintenance activities at Yongbyon," a spokesman quoted Defence Minister Kim Tae-Young as telling Parliament on Monday.
"It is engaged in new construction and large-scale excavation," he said.
An unidentified government official was quoted by Dong-A Ilbo newspaper as saying that two rectangular buildings were being built next to the site of a cooling tower demolished in 2008.
A private US research institute reported last week that new construction or excavation was under way at Yongbyon near the site of the former cooling tower.
The Washington-based Institute for Science and International Security (ISIS) said tracks made by heavy machinery along with construction or excavation equipment were visible in satellite photos.
ISIS said there appeared to be ongoing construction of two small buildings next to the site of the cooling tower at Yongbyon. The North blew up the tower in June 2008 in front of foreign media to dramatise its commitment to nuclear disarmament.
The institute said the purpose of the work is unclear but bears watching.
Yongbyon was the source of plutonium for an atomic weapons programme. The country`s stockpile is believed to be enough for six to eight bombs.
North Korean Vice Foreign Minister Pak Kil-Yon told the United Nations last week his country must strengthen its nuclear deterrent in the face of what he called threats from the United States.
The North shut down Yongbyon in July 2007 under a six-nation aid-for-disarmament accord. The following summer it destroyed the cooling tower.
But six-party talks bogged down in December 2008 over ways to verify the North`s denuclearisation. In April 2009, Pyongyang abandoned the talks and said it had resumed reprocessing spent fuel roads to make weapons-grade plutonium.
In May 2009, it conducted an atomic weapons test, its second.
The North has indicated willingness in principle to return to the six-party talks. But it says it wants separate talks with the United States about signing a permanent peace treaty on the peninsula.