President George W Bush welcomed South Korean President Roh Moo-Hyun to the White House today for crucial and hugely anticipated talks heralded by communist North Korea with a new round of nuclear sabre-rattling.

This first encounter between Bush and Roh, which will also mark the 50th anniversary of the US-South Korea alliance, is seen as critical to framing a joint strategy to contain Pyongyang's nuclear challenge.

It will be closely watched for signs of a personal connection between Bush and his untested visitor, who took office earlier this year and will be making his debut on the international stage.

Bush had notoriously frosty relations with Roh's predecessor Kim Dae-Jung, which never fully thawed following a tense White House summit in March 2001 and soured joint diplomatic attempts to confront Pyongyang.

"President Bush likes personal meetings to get a personal assessment of another leader, (to) develop a personal relationship," said a White House official on condition of anonymity.

The US leader famously seeks to size up fellow statesmen, and it is often clear in public appearances whether he makes a true connection with a foreign "friend" or struggles to get along.

Both sides are likely to declare the meeting a success, as both have a large stake in a workable relationship between Seoul and Washington.

Roh will be keen to make a good first impression, after admitting in newspaper interviews here that some US observers, who watched his election campaign exploit anti-US demonstrations in South Korea last year, have little idea of his character.

Ahead of the talks, he has staked out a tough position on North Korea, perhaps seeking to score early points with the Bush administration, which pioneered a hawkish line towards Pyongyang, ruffling feathers in Seoul.

Roh said in a speech yesterday, "North Korea must give up its nuclear program without fail so it can become a responsible member of the international community".

The South Korean leader warned Monday that nuclear arms development would lead North Korea down a "blind alley".

But significant differences remain between Washington and Seoul on how to handle the North Korean nuclear crisis, which has escalated steadily since October when the US accused Pyongyang of pursuing a covert uranium enrichment plan in violation of a 1994 anti-nuclear pact.

Roh has insisted that the option of military force is untenable, given the fact that Seoul, which lives under threat from thousands of artillery tubes and North Korean missiles, could be an early target of any retaliatory punch from Pyongyang.

While stressing repeatedly that it wants to solve the North Korean crisis peacefully, the Bush administration has said all options remain on the table.

South Korea is also wary of a hawkish stream of opinion in Washington, which would like to see Pyongyang further isolated in an economic and diplomatic squeeze designed to throttle Kim Jong-Il's regime.

Seoul is horrified at the prospect of a collapse of North Korea, and the likely mass exodus of malnourished and bewildered refugees that would likely follow.

The White House sees the Roh talks in the context of further meetings at Bush's Camp David retreat next week with Japan's Prime Minister Junichiro Koizumi.

"We are going to discuss the situation with the Japanese, too," said the official.

"We are consulting with allies to determine the way forward with respect to North Korea".

The US has tried to ensure that steps to end the crisis involve other key Asia-Pacific powers, and has insisted that any further talks like those in Beijing last month in which it joined China and North Korea must also include Japan and South Korea.

North Korea is also closely watching developments in Washington.

It marked the run-up to the talks by declaring a 1992 anti-nuclear deal with South Korea as "a dead document" and blamed Washington for its demise.

But deputy US State Department spokesman Philip Reeker described the move as a "regrettable step, we believe in the wrong direction". – Sapa.