The South Korean government admitted Thursday it extracted "several milligrams" of plutonium during a research experiment in 1982.

The experiment was done between April and May of 1982 at a research reactor of Korea Atomic Energy Research Institute (KAERI), then based in Seoul, said the South Korean Science and Technology Ministry.

Earlier Thursday, South Korean Yonhap News Agency quoted an official at the Foreign Ministry as saying the International Atomic Energy Agency had started investigation on the plutonium extraction experiment.

The KAERI moved to Daejeon, some 160 kilometers south of Seoul, in 1984, and the reactor has been dismantled since then.

The fresh revelation came a week after Seoul admitted several South Korean scientists obtained 0.2 grams of enriched uranium from a one-off experiment in 2000 without reporting to the United Nations nuclear watchdog.

Plutonium and enriched uranium are the two main types of fissile material used in nuclear weapons.

However, the South Korean government denied it has nuclear weapon program and said Seoul will stick to nuclear non-proliferation commitment.