South Korean officials are concerned that their admission of uranium production may upset U.S.-led international efforts to dismantle North Korea's nuclear weapons programs that have raised tensions in the divided peninsula.

The acknowledgement of the uranium test at government-run nuclear facilities has surprised the international community and triggered suspicions that the country may have attempted a secret program to counter North Korea's nuclear threats.

Some foreign news reported that the uranium obtained was almost pure enough for an atomic bomb, which prompted calls from close ally the United States for a thorough investigation. If highly enriched, uranium is used for manufacturing nuclear warheads.

Analysts here also express concerns the uranium test could give North Korea an excuse to further delay the already stalling six-nation negotiations aimed at ending its nuclear drive and move ahead with its own nuclear weapons drive. North Korea is believed to have a secret nuclear weapons program based on highly enriched uranium in addition to its plutonium-based program.

At a hurriedly arranged media conference on Friday, senior officials from the Foreign Ministry and the Science and Technology ministry flatly denied harboring any nuclear weapons ambitions.

Only a small amount of uranium was produced during an unauthorized test in early 2000 at a government laboratory for nuclear energy research, officials said. They denied it was aimed at producing nuclear weapons.

South Korea has never had enrichment or nuclear reprocessing programs, let alone a weapon program, said Oh Joon, director general for international organizations at the Foreign Ministry.

Since this is a one-time isolated scientific experiment, not part of any weapons program, we think this should not have any impact on the ongoing six-nation talks on North Korea's nuclear issue, Oh said.

The experiment involved separating 0.2 grams of uranium, officials said. It took place in January-February 2000 at the government-run Korea Atomic Energy Research Institute in Daejeon, 99 miles south of Seoul,

The scientists, dedicated to research on nuclear fuel, carried out the experiments of laser isotope separation on materials such as gadolinium, thallium, samarium and also a small amount of uranium, said Cho Chung-won, the nuclear bureau chief of the Ministry of Science and Technology.

The separated uranium was not weapons-grade. How we can make bombs with just 0.2 gram of uranium acquired by a one-off experiment? he asked. It was not enrichment of uranium, but just a one-time separation.

All experiment-related activities were terminated, and the equipment used was dismantled immediately afterward, Cho said. The obtained uranium is carefully kept in the laboratory.

The government voluntarily reported the experiment to the International Atomic Energy Agency on Aug. 17, and the U.N. nuclear watchdog has investigated the case this week, officials said.

A nine-member IAEA inspector team completed a weeklong investigation into the uranium test on Friday. They are due to return to the headquarters in Vienna.

Seoul officials said it is up to the U.N. nuclear watchdog to rule whether its uranium experiment violated its nonproliferation obligations. We have to wait and see, Cho said.

He said research facilities, such as the government-run nuclear laboratory, were not subject to compulsory reporting to the IAEA four years ago, when the experiment was conducted, but became so under the additional protocol to the Nuclear Nonproliferation Treaty, which the country adopted in February this year.

The government became aware of the uranium test only this month while preparing a report to the IAEA as required under the additional protocol, Cho said. We decided to make public the experiment in a transparent manner to avoid unnecessary misunderstanding, he said.

The fact that we have decided to report this faithfully and transparently to the IAEA reflects our commitment to nuclear nonproliferation, Cho said. We are sincerely honoring our obligations for the peaceful use of nuclear energy and nuclear nonproliferation.

The discovery could lead to calls for South Korea to be referred to the U.N. Security Council, like North Korea, but foreign ministry officials said the issue would not be dealt with at the upcoming assembly that begins on Sept. 20.

Nuclear experts in Seoul also ruled out South Korea's nuclear ambitions. An extremely small amount, 0.2 gram, falls much short of producing an atomic weapon, said Hwang Yong-sul, a nuclear science professor at Seoul National University.

Some 25 kilograms of enriched uranium with a 90 percent concentration of uranium 235 isotope is needed to produce one uranium bomb, he said. Only 15 kilograms is necessary if the concentration is close to 100 percent.

But analysts here voice concerns that North Korea can use the uranium test as a pretext to stall international talks on its nuclear weapons drive. We are concerned that North Korea may use this case as a card in future negotiations, a Unification Ministry official said.

North Korea has made no response yet to the South's uranium test. On Friday, it repeated its threat to building a nuclear deterrent to counter what it calls plans by the United States and its South Korean ally to unleash a nuclear war on the divided Korean peninsula.

The United States, the two Koreas, Japan, China and Russia have agreed to resume the six-nation negotiations on the North's nuclear programs by the end of the month, but no date has been announced.