South Korea told the IAEA in August that it had failed to declare nuclear activities, including uranium conversion, uranium enrichment and plutonium separation.

Seoul says the experiments were conducted, without the government's knowledge, for academic purposes by ambitious scientists and started in the early 1980s.

The IAEA immediately sent inspection teams to South Korea and has just published an eight-page confidential report on their findings.

The report says the quantities of nuclear material used in the experiments were not significant, but the nature of the activities and the failure to declare them is a matter of serious concern. It says a tiny amount of uranium was enriched that came close to bomb-grade material.

Inspectors visited several sites in South Korea and photographed dismantled equipment and interviewed scientists.

The IAEA praised Seoul for active cooperation with the agency's inspectors.

South Korea says it is committed to keeping the Korean peninsula free from nuclear weapons and is not interested in a uranium enrichment program.

Gary Samore, former U.S. official and head of the International Institute for Strategic Studies, says he believes this to be the case.

"Technically, there's no question that South Korea has the basic scientific and industrial infrastructure to produce nuclear weapons if they wanted to, that's not a surprise; it's a very advanced country," said Gary Samore. "The only question is whether a political decision is made on the part of the South Korean government and I don't see the South Korean government at this point making such a decision and it appears as though these experiments were very much curiosity on the part of the South Korean scientists."

The IAEA says it still has to verify some of the evidence collected during its investigation and is calling for more documentation from Seoul.

The 35-member IAEA board of governors meets in Vienna November 25 and will decide if South Korea's failures amount to a violation of the Nuclear Non-Proliferation Treaty.