The International Atomic Energy Agency (IAEA) is to send a second inspection team to locations where South Korea has belatedly admitted that scientists engaged in undeclared nuclear experiments.

"The experiments have nothing to do with the enriching (uranium) or reprocessing (plutonium) programs for developing nuclear weapons," Ban told a weekly briefing.

"I'm confident that IAEA investigations will prove the fact that our government is firmly committed to its non-proliferation policy."

IAEA inspectors are due to visit two state nuclear research centers where South Korean scientists extracted a small amount of plutonium in 1982 and enriched a small quantity of uranium in 2000.

The inspectors will begin work on Monday and report back to headquarters in Vienna before a new board meeting of the UN atomic watchdog next month.

The visit is a follow-up to the initial probe two weeks ago by the UN watchdog.

The IAEA said Monday that 150 kilograms (330 pounds) of uranium metal was produced in undeclared conversion activities in the early 1980s and a small amount of this was used in 2000 to produce the enriched uranium.

IAEA chief Mohamed ElBaradei expressed "serious concern" about the activities but South Korean officials played down his comment as standard.

Seoul says the experiments were purely for academic research but has yet properly to clarify why the production of uranium metal was undeclared.