South Korea brushed off a television report Tuesday that North Korea is preparing for a third nuclear test, amid heightened cross-border tensions over the sinking of a South Korean warship last month.

South Korean YTN TV, quoting an unidentified diplomatic source in Beijing, said North Korea had begun the preparations in February for a test possibly in May or June.

But South Korean Foreign Minister Yu Myung-Hwan told journalists: "There are no signs of the North preparing for a third nuclear test."

Analysts in Seoul also dismissed the report as implausible.

YTN TV had said the preparations involved significantly upgraded technology compared with its previous two tests. It said Pyongyang had been receiving technological assistance from Russians and that a senior North Korean official recently visited Beijing to discuss a possible test.

North Korea carried out its first nuclear test in 2006 and a second in May last year, after it walked out of six-party nuclear disarmament talks.

Analysts in Seoul said however that the isolated communist state had little reason to carry out another nuclear test at a time when its ally China is struggling to revive the stalled disarmament talks.

Baek Seung-Joo of the prestigious Korea Institute for Defence Analyses told AFP the TV report was "like a novel," saying Russia and China were dedicated to global efforts to prevent nuclear proliferation.

South Korea warned on Tuesday however that a resumption of the six-party talks may not be possible if Pyongyang is found to have been involved in the sinking of one of its warships last month.

China is the host of the talks aimed at persuading North Korea to abandon its nuclear weapons programmes in return for diplomatic and economic gains. The forum also includes the two Koreas, Japan, Russia and the United States

Yang Moo-Jin, professor of the University of North Korean Studies, also dismissed the YTN report as "totally implausible."

"There is no reason for the North to carry out a third nuclear test at this time when the host China is making utmost efforts to resume the six-party talks," Yang said.

North Korea has said it will not return to the nuclear talks programme until UN sanctions are lifted and the United States commits to holding talks on a formal peace treaty to end the 1950-53 Korean War.

earlier related report
Seoul warns on nuclear talks if N.Korea linked to sinking
Seoul (AFP) April 20, 2010 - South Korea warned Tuesday that stalled North Korea nuclear disarmament talks would not resume if it finds the communist state was involved in the sinking of one of its warships.

The downing of a 1,200-tonne corvette in the Yellow Sea last month after a mystery blast has ratcheted up cross-border tensions, with suspicions hanging over North Korea although Seoul has not directly accused Pyongyang.

"If convincing evidence of North Korea's involvement is found, I think the six-party talks will be unable to take place for the time being," Foreign Minister Yu Myung-Hwan told a briefing.

Adding to the jitters, a South Korean television station said North Korea was preparing a third nuclear test, but Yu dismissed the report and analysts also described it as implausible.

Yu however said that if Pyongyang is clearly found to be responsible for the March 26 disaster which cost the lives of 46 sailors, "the North would then have to be called to account over the sinking".

As well as warning about the future of the stalled nuclear talks, he repeated comments made Sunday that Seoul would take the issue to the UN Security Council for possible sanctions if Pyongyang was involved.

South Korean officials say an external explosion was the most likely cause, but have refrained from directly pointing the finger at the reclusive communist state.

President Lee Myung-Bak vowed Monday a "resolute" response to the disaster, the worst peacetime loss of life for South Korea's navy.

Pyongyang on Saturday denied any involvement, accusing the conservative South Korean government of seeking to shift the blame in order to justify its hardline policy toward the communist North.

Analysts said the incident could harm diplomatic efforts aimed at coaxing North Korea back to the six-party nuclear disarmament talks it quit a year ago.

"South Korea may take strong diplomatic measures or ask for a delayed six-party forum if there is clear evidence of North Korea's involvement," Seoul's Dongguk University professor Kim Yong-Hyun told AFP.

Foreign Minister Yu dismissed a report by South Korean YTN TV that the North was preparing a third nuclear test following ones in 2006 and 2009.

"There are no signs of the North preparing for a third nuclear test," he said.

Quoting an unidentified diplomatic source in Beijing, YTN said the North had begun the preparations in February, involving significantly upgraded technology, for a test possibly in May or June.

Yang Moo-Jin, professor of the University of North Korean Studies, also dismissed the YTN report as "totally implausible."

North Korea has said it will not return to the nuclear talks programme until UN sanctions are lifted and the United States commits to holding talks on a formal peace treaty to end the 1950-53 Korean War.

With the cloud of suspicion hanging over North Korea over the sinking, South Korea is launching detailed inspections of the Cheonan after the broken wreckage was moved ashore.

"Naked-eye inspections of the stern have led the joint investigation team to a conclusion that an outside explosion was a high possibility," defence ministry spokesman Won Tae-Jae told journalists.

"But any conclusive findings would come only after we salvage and inspect the bow section and other debris," he added.

Efforts to recover the still-submerged bow resumed after the salvage was hampered when a chain snapped under pressure from high waves and strong currents.

The bow is expected to be brought to the surface by this weekend if weather conditions are favourable. Salvage ships and mine sweepers have also been combing the sea in the hunt for debris.

Seoul has set up a 69-member investigation team which will eventually include 15 US and other foreign experts in a bid to ensure the eventual findings cannot be disputed.

Yoon Duk-Yong, co-head of team, said Friday that the warship appeared to have received a powerful impact on the port side, where steel plate was curved inwards, and ruled out an onboard blast.