Faced with mounting suspicion over the undeclared experiments, government authorities took pains to stress the amount of enriched uranium was "smaller than a sesame grain" and far short of weapons grade.

In a bid to calm international concern, the government reportedly plans to repeat its pledge that South Korea has no nuclear arms programme and that it will never pursue one.

Revelations that South Korean scientists had engaged in clandestine uranium enrichment emerged at a time when Seoul is playing a leading role in efforts to end North Korea's nuclear weapons drive.

A team of inspectors from the International Atomic Energy Agency (IAEA) on Saturday completed a week-long inspection of Korea Atomic Energy Research Institute (KAERI), where the tests were carried out.

They will report to IAEA director general Mohamed ElBaradei about their findings at the state-financed research institute in Daejeon, 160 kilometers (100 miles) south of Seoul upon their return to Vienna next week.

ElBaradei will inform the board of governors of the IAEA's initial findings at a meeting that is expected to last for three days, the nuclear watchdog said.

"We will explain our position very clearly at the IAEA board of governors meeting and seek their understanding," Ban said after a standing committee meeting of the National Security Council here Saturday.

Ban said the government would do its utmost to clear suspicions about the experiments raised by some foreign news media.

KAERI president Chang In-Soon brushed aside as "totally groundless" reports that the enriched uranium was close to weapons grade.

"The uranium separated at that time had a concentration ratio of some 10 percent," he was quoted as telling the Chosun daily.

"Aside from its low concentration, the quantity of uranium involved is so miniscule that it is just unimaginable that the experiments were carried out for any purposes other than research," he said.

For weapons use, scientists said natural uranium should be enriched so its U-235 concentration is higher than 90 percent, with at least 10 kilogramspounds) required for one bomb.

The Science and Technology Ministry said the 0.2 grams (0.007 ounces) of enriched uranium, produced during a one-off experiment using laser isotope separation technology in January and February 2000, had been safely stored and accounted for at KAERI, Chang said.

"Some news media suggested this experiment might be a step to build nuclear weapons, but any atomic energy experts would laugh at such claims," Chang said.

He said the test had been conducted "out of curiosity" by a few scientists who were using laser isotope separation equipment to extract gadolinium, a cooling material used at nuclear power plants.

The equipment used for the tests has also been dismantled and stored at KAERI, he said.

IAEA said South Korea informed it on August 23 that it had enriched nuclear material in the course of experiments that had not been declared to the agency.

The information was given to IAEA during discussions about South Korea's initial declarations which should be made under the Additional Protocol to its Safeguards Agreement.

The Additional Protocol did not take effect until February after Seoul ratified it, binding itself to strengthened regulations on nuclear material.

South Korean officials told IAEA the experiments were carried out without the government's knowledge and had been terminated.