South Korea says it made a mistake by not reporting a uranium experiment to the United Nations agency that oversees nuclear activities. The statement comes nearly a week after Seoul acknowledged that its scientists had produced a small amount of enriched uranium four years ago.

A day before officials leave for the headquarters of the International Atomic Energy Agency, the South Korean government conceded that it should have reported the uranium test done in 2000. The government earlier insisted that it did nothing wrong by failing to report the production of enriched uranium.

Oh Joon, the director general of international organizations for South Korea's Foreign Ministry, says the country should have informed the IAEA about the unauthorized experiment.

"This matter should have been reported to the IAEA because we have an agreement with IAEA, according to which we are supposed to report on any nuclear material we have. So there was a failure of reports," he said.

Mr. Oh says South Korea will explain to the IAEA board members next week in Vienna that this was an isolated experiment and not part of any clandestine nuclear weapons development program.

The board will decide if South Korea violated rules to prevent the spread of nuclear weapons and whether it should punished.

Mr. Oh and other South Korean officials say they have been surprised by the international reaction, and contend media reports have been overblown.

They say the small amount of uranium enriched by lasers was not enough to make a nuclear weapon, nor was it of the right quality. But some Western diplomats in Vienna contend the enriched uranium was close to weapons grade.

The revelation has been an embarrassment for South Korea as it tries to play a leading role in multinational negotiations to get rival North Korea to end its nuclear weapons programs.

A fourth round of talks, involving both Koreas, the United States, China, Japan and Russia are supposed to be held in Beijing this month, but no date has been set.

Some participants are worried that communist North Korea will use the news of the South Korean uranium experiment as an excuse to delay further discussions.