In Vienna, Mohamed ElBaradei, head of the International Atomic Energy Agency (IAEA), said Monday that Seoul recently acknowledged producing more than 150 kilograms of uranium metal in the 1980s at three facilities it had kept secret from his agency.

He made the remarks in an opening speech at the agency's Board of Governors meeting in Vienna on Monday.

ElBaradei also told reporters that South Korea's failure to report what it called unauthorized experiments that led to plutonium extraction and uranium enrichment were a "matter of serious concern."

He said he would have a broader report on Seoul's clandestine nuclear activities by the next board meeting in November.

The IAEA chief said he hoped to assure the world that the experiments were "isolated activities and that all measures are being taken" by Seoul so that they do not recur.

Reiterating Seoul's stance on the matter, South Korean delegate Cho Chang-bom told reporters the experiments involved only minute quantities of enriched uranium and plutonium, and were performed by a small group of renegade scientists "without the knowledge and authorization of the government." He said that with the revelations now public, South Korea harbors no more nuclear secrets.