South Korea's deputy assistant unification minister Park Chan-Bong met US congressional aides Keith Luse and Frank Jannuzi, who arrived here Sunday after a five-day trip to North Korea, Park's office said.

Luse and Jannuzi, along with US nuclear experts, inspected the nuclear complex at Yongbyon, 90 kilometers (50 miles) north of Pyongyang, at the center of a 15-month crisis over North Korea's nuclear weapons drive.

They were the first outsiders allowed into Yongbyon since North Korea expelled UN inspectors in response to the cancellation of US fuel oil shipments to the energy-strapped country in December, 2002.

The two are scheduled to meet Wi Sung-Lac, head of the foreign ministry's North American bureau, later in the day.

South Korean officials remained tight-lipped on talks between Park and the US delegates who have declined to speak to the media about what they saw at Yongbyon.

North Korea said Saturday it showed its "nuclear deterrent" to the unofficial US delegates.

US newspapers said the delegates appeared to have seen reprocessed plutonium, an ingredient for making nuclear bombs, although Luse referred to the US and North Korean reports as speculative and warned against drawing "premature" conclusions.

Analysts and officials here said the tour was intended to show the United States that North Korea was pushing ahead with its drive to become a nuclear power.

North Korea's claims that it reprocessed 8,000 spent nuclear fuel rods, which would yield enough plutonium for up to six nuclear bombs have been met by scepticism here and in Washington.

"North Korea appeared to have opened up its facilities with the intention of proving (to outsiders the truth) of what it has been saying," Kim Hee-Sang, presidential advisor for national defense, told reporters.

South Korea's main opposition Grand National Party said that the demonstration proved that President Roh Moo-Hyun's efforts to stop North Korea's nuclear weapons program had failed.

"The security balance on the Korean peninsula has now been disrupted," the conservative party said.

North Korea agreed in 1994 to mothball its Yongbyon complex but fired up the facilities after the latest nuclear crisis erupted in October 2002.

North Korea later said it completed reprocessing 8,000 spent fuel rods at Yongbyon, which had been sealed and placed in cooling ponds in 1994.

North Korea offered last week to refrain from producing and testing nuclear weapons in what it said was a "bold concession" to the United States, in return for concessions from Washington..

Efforts to reconvene the nuclear crisis talks following the inconclusive first round in Beijing last August have so far failed amid differences over the scope of negotiations.

But Chinese State Councilor Tang Jiaxuan told visiting Japanese lawmakers in Beijing that he expected the second round of six-way talks to resume in February, according to Japanese newspapers.

Tang has reportedly said the nuclear crisis would not be resolved unless economic aid including energy is provided to the impoverished country.

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