The head of the United Nations nuclear agency is in Seoul, South Korea, to discuss the country's past unauthorized nuclear experiments.
Mohamed ElBaradei, the director of the International Atomic Energy Agency, said Sunday his agency needs to make sure that such instances of undisclosed nuclear research are not repeated. He will hold a series of meetings with top South Korean officials over the next several days.
Mr. ElBaradei's visit follows South Korea's recent admission that scientists had extracted a small amount of plutonium in the early 1980s and conducted experiments to enrich uranium in 2000.
South Korea insists the experiments were purely scientific in nature.
North Korea said Saturday there will be no more bilateral talks with South Korea unless the South's nuclear experiments are thoroughly investigated.