The experiment conducted in January 2000 at the country's state-run nuclear research center produced a miniscule amount of enriched uranium.

Until now, the government has argued that it saw no wrongdoing despite its failure to report the experiment that produced 0.2 grams (0.007 ounces) of uranium to the UN's nuclear watchdog.

The government is now stepping back from that position, an official told Yonhap.

"The 0.2 grams of extracted uranium should have been reported although the experiment itself and facility had not to be reported," the unnamed official was quoted as saying ahead of a briefing to journalists later in the day.

International Atomic Energy Agency (IAEA) staff inspected the research center in South Korea last week where the experiment took place and returned to Vienna with a sample of the enriched uranium.

South Korea will dispatch a team of officials to Vienna to attend a four-day board meeting of the IAEA starting Monday that will consider the case.

They will argue vigorously that the experiment was conducted for purely academic purposes and was in no way linked to nuclear weapons ambitions.

"The government has maintained transparency and reliability in its non-proliferation policy by voluntarily declaring it and fully cooperating with the IAEA inspection," South Korean Foreign Minister Ban Ki-Moon said in a weekly briefing.

Ban said he expected "the IAEA to handle the case in a factually-correct and balanced manner" at its board meeting.

Revelations that scientists in South Korea engaged in clandestine uranium enrichment embarrassed officials here at a time when Seoul is playing a leading role in efforts to end North Korea's nuclear weapons programme.

However, the government until now has rejected charges it violated its international obligations, claiming that there was no stipulation at the time under the nuclear Non Proliferation Treaty (NPT) to report the enrichment activities.

Seoul argued it was only obliged to report the enrichment activities after new, tougher safeguards came into force under an additional protocol to the treaty that came into force in February.

In any case, the government said that it was not told about the experiment at the time and was only informed in August by scientists at the Korea Atomic Energy Research Institute in Daejeon, 160 kilometers (100 miles) south of the capital.

The experiment using laser isotope separation technology was a "one-off" case and South Korea has no interest in running a nuclear weapons programme, the government maintained.

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