The UN's nuclear watchdog says that South Korea's failure to report secret nuclear research is "a matter of
Seoul's nuclear revelations shocked the region
International Atomic Energy Agency chief Mohamed ElBaradei said he would continue to investigate Seoul over its uranium and plutonium experiments.
South Korea admitted last week that some of its scientists had conducted clandestine nuclear experiments.
The US had already chastised Seoul for its failure to report the infringement.
Mr ElBaradei told a meeting of IAEA governors that he would report on the investigation by the board's next meeting, in November.
"I would ask the Republic of Korea to continue to provide
active cooperation and maximum transparency in order for the
agency to gain full understanding and scope" of the research,
Mr ElBaradei said.
South Korea - a strong ally of the US in its continuing quest to get North Korea to give up its nuclear ambitions - stunned the region on 2 September when it revealed that, like its neighbour, it too had fallen foul of international nuclear accords.
A small number of South Korean scientists had conducted secret tests to produce 0.2g of enriched uranium in 2000, the government admitted.
It said the experiments were not authorised by the authorities, and were conducted for South Korea's civilian nuclear power industry.
Last week Seoul also admitted extracting a small amount of plutonium - a key ingredient in nuclear bombs - in secret research conducted in the early 1980s.
An official from South Korea's science and technology ministry, Kim Young-shik, said scientists had conducted the experiment out of academic curiosity, and that South Korean officials had already held talks with the IAEA about the issue.
South Korea's ambassador to the IAEA, Cho Changbeon, insisted on Monday that there would be no further revelations of illicit nuclear tests.
"I think I can safely say that, according to the investigations
the South Korean government has conducted, there are no other such similar experiments on enrichment or processing," Cho Changbeon told the French news agency AFP.