Four inspectors from the U.N. nuclear watchdog agency began additional investigations Monday into South Korea's (search) past secret nuclear experiments, officials said.
Last month, the Vienna, Austria-based International Atomic Energy Agency (search) decided not to refer the issue of South Korea's nuclear experiments to the U.N. Security Council (search), which could have imposed punitive measures.
Still, the IAEA's board of governors criticized South Korea for conducting plutonium and uranium experiments in 1982 and 2000 without reporting them to the agency.
The government has repeatedly said the experiments were unrelated to any weapons program and were for scientific research only.
The inspection team, which arrived Sunday, also planned to participate in a meeting this week between South Korea and the IAEA to discuss ways to enhance inspections, a South Korea Science and Technology Ministry official said on condition of anonymity.
The visit is the fourth by IAEA inspectors since South Korea revealed experiments earlier this year.
Plutonium and enriched uranium are key ingredients in nuclear weapons, and revelations about the experiments threatened to hobble international efforts to persuade the South's rival, North Korea, to curb its nuclear ambitions.
However, the amounts used in South Korea's experiments were far below that required to make weapons.
North Korea vowed last week to make the South's past experiments a top priority for discussion in six-nation nuclear talks, which include the United States, aimed at ending the North's nuclear weapons programs. No date has yet been set for resumption of those meetings, which so far have not led to any breakthroughs.