A week after admitting government scientists enriched uranium in a clandestine experiment four years ago, South Korea has revealed it also engaged in plutonium research more than 20 years ago.
South Korean officials on Thursday confirmed that several milligrams of plutonium were extracted in a 1982 experiment at the country's nuclear energy research institute.
A week ago, South Korea revealed that in 2000, government scientists enriched a small amount of uranium.
South Korean diplomats insist the experiments were extremely limited and conducted purely for scientific research. But many are skeptical about that explanation, including Professor Katsuya Kodama, the secretary-general of the International Peace Research Association in Japan.
"The purpose of having that kind of experiment is to ensure the capacity of making nuclear weapons in a short time," said Katsuya Kodama.
Plutonium and enriched uranium are the two primary materials used to make nuclear bombs.
A team of inspectors from the International Atomic Energy Agency visited South Korea last week to investigate the country's unauthorized nuclear activities. The findings will be discussed at a board meeting of the U.N. agency next week.
The timing of the revelations could hurt sensitive negotiations on North Korea's nuclear weapons programs. South Korea has joined the United States, China, Japan and Russia for three rounds of talks with North Korea aimed at ending Pyongyang's nuclear weapons ambitions.
Communist North Korea on Wednesday said South Korea's uranium enrichment could trigger a regional arms race.
South Korea ratified the Nuclear Non-Proliferation Treaty in 1975. North Korea signed it in 1985 but withdrew from the pact in January of last year. Member states of the treaty pledge not to develop nuclear weapons.