North Korea has amassed a "considerable" amount of enriched uranium, a high profile defector was quoted as saying on Thursday.
Hwang Jang-Yop told South Korean lawmakers that the communist state completed preparations for an underground nuclear test in 1996.
"As far as I know it has piled up a considerable amount of enriched uranium," he told a meeting hosted by the minor opposition Liberal Forward Party (LFP), a party spokesperson said.
The LFP's Park Sun-Yong also quoted Hwang, 85, as saying the North's recent move to restart its nuclear weapons programme was a bargaining tactic to earn concessions from Washington.
Hwang, former secretary of the North's ruling Workers' Party and an ex-tutor of leader Kim Jong-Il, defected during a trip to Beijing in 1997. He remains under police guard at a secret address in South Korea.
The South and the United States, along with China, Japan and Russia, have been negotiating nuclear disarmament since 2003 with North Korea, which tested an atomic weapon in October 2006.
The United States accuses the North of developing a secret highly enriched uranium weapons programme, a charge it denies.
The North has told the International Atomic Energy Agency (IAEA) it would start work to resume plutonium reprocessing at its Yongbyon complex, possibly within a week. It has barred IAEA from the reprocessing plant.
Analysts in Seoul say the North is practising brinkmanship in its bitter dispute with Washington over nuclear inspections, but is not necessarily bluffing.