Chung Woo-Seong, advisor to President Roh Moo-Hyun on foreign affairs, said the recently revealed experiments in 1982 and 2000 were merely on a laboratory scale and the government had no role in them.

"These experiments have no relevance to the six-nation talks on North Korea's nuclear programme," Chung said on a radio talk show.

"The experiments were merely on a laboratory scale and the government had no roles in the experiment," Chung said by phone on the MBC radio talk show from Moscow. Chung is accompanying Roh, who is visiting Russia.

Chung said Roh had explained this to President Vladimir Putin and briefed him on South Korea's renewed promise not to develop or possess nuclear weapons. Putin expressed his "understanding", according to Chung.

But in an apparent rap on the knuckles from Moscow, the Russian foreign ministry Wednesday called on Seoul to cooperate fully with international experts investigating the experiments.

"The Russian side stressed our interest in ensuring that the Republic of Korea cooperates in an open and transparent manner with the IAEA" in its investigation of the experiments, the ministry said in a statement.

China's Foreign Ministry spokesman Kong Quan reportedly said Tuesday that the nuclear experiments by South Korea should also be on the table at the six-nation talks.

Investigators from the UN nuclear watchdog began a week-long investigation into the experiments on Monday after Seoul renewed a pledge never to develop atomic weapons.

Earlier this month, as a first team of International Atomic Energy Agency (IAEA) inspectors was visiting South Korea, the government revealed that its scientists secretly enriched a small amount of uranium in 2000.

Then came revelations that scientists had extracted a tiny amount of plutonium in 1982.

South Korea insisted the experiments were not linked to nuclear weapons programs. IAEA chief Mohamed ElBaradei, however, expressed "serious concern" about the activities.

The new inspection team will report back to the Vienna-based IAEA by November after interviewing scientists engaged in nuclear experiments.

A senior official of the ruling Uri Party said South Korea would go the extra mile to ensure transparency in its nuclear activities.

"South Korea is ready to stand naked before inspections," Chun Jung-Bae, majority leader of the National Assembly, told reporters.

On Saturday South Korea made a fresh pledge that it would not develop or possess nuclear weapons but would pursue scientific research transparently.

The case, however, has already damaged multilateral efforts to persuade Stalinist North Korea to give up its nuclear weapons programs.

Pyongyang's official KCNA news agency warned Saturday that the communist country would not abandon its nuclear ambitions. It also said North Korea would not attend the six-nation talks on its nuclear program unless South Korea cleared up suspicions over its nuclear experiments.

A fourth round of the six-nation talks was scheduled for this month but China has admitted it would be difficult to hold them by the end of September as planned.

Apart from the two Koreas, the talks include China, the United States, Russia and Japan.

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