By Charles Scanlon
BBC News, Seoul
Talks on North Korea's nuclear weapons programme resume in Beijing this week in what could be a final chance to secure a diplomatic solution.
52 years on, North and South Korea are still technically at war
Failure to make progress will increase pressure in the US for referral to the UN Security Council and possible sanctions.
After nearly three years of deadlock, the gulf of mistrust between North Korea and the US appears as wide as ever.
But there's a new sense of urgency, following North Korea's declaration in February that it had nuclear weapons and was building more.
One former US official derided the three previous rounds of the six-party talks as "drive-by meetings", rather than a serious effort to test North Korea's intentions and explore the possibility of a negotiated solution.
This time, the US has agreed to a more flexible format with open-ended talks and more scope for bilateral meetings - a longstanding North Korean demand.
That could mark a significant change in Washington's approach.
It initially saw the six-party format as a mechanism to increase regional pressure on North Korea and to drive home the demand for "the complete verifiable and irreversible dismantlement" of all its nuclear facilities.
But South Korea and China resisted what they saw as a hardline American policy that could provoke a dangerous confrontation.
Some analysts say the US has been forced on to the defensive - obliged to show the region that it is serious about negotiations, and anxious not to take the blame should dialogue break down.
At the last round of talks in June 2004, US officials made an offer that remains on the table.
N Korea blamed US policies for the suspension of talks
It included security guarantees and the prospect of economic aid - but only if North Korea made the first move by declaring an intention to give up all its nuclear capabilities.
That offer is now likely to be sweetened by a South Korean initiative to supply 2,000 megawatts of electricity to the power-hungry North.
It's unclear how North Korea will react to a plan that would make it dependent on the South for a significant part of its electric power.
The North says it is committed to the denuclearisation of the Korean peninsula. But that includes a demand for the removal of the American nuclear threat - something the US is not prepared to discuss at these talks.
North Korea has offered to freeze its plutonium production facilities at Yongbyon in return for a reciprocal package of economic and diplomatic incentives.
But the US says a freeze is not enough.
And there's little sign of movement on a key stumbling at the previous rounds - a fundamental disagreement over the scope of the North's nuclear facilities.
It angrily denied American allegations that it's running a second secret weapons programme based on highly enriched uranium (HEU).
It was the Bush administration's challenge to North Korea over that programme that led to the current confrontation, and persuaded the North to crank up its moth-balled plutonium plant at Yongbyon.
"That's one of the toughest issues," said a senior South Korean official, who asked not to be identified.
"The question is how we put it on the table...one issue should not be allowed to impede all the others".
The US Secretary of State, Condoleezza Rice, said on a recent visit to Seoul that the US would continue to stress the alleged uranium programme.
North Korea was brought back to the negotiations after a 13-month hiatus by a combination of US threats, and persuasion from China and South Korea.
In recent days, it's listed a string of demands, including the establishment of diplomatic relations with Washington, an end to sanctions and the signing of a peace treaty to replace the Korean War armistice of 1953.
Some analysts see it as an attempt to cloud the agenda and buy more time.
South Korea is warning against high expectations, but says there are grounds for cautious optimism.
"We don't know exactly what North Korea will come up with this time - but we have strong expectations they will be more forthcoming because of the recent progress in North-South dialogue," said the South Korean official.
North Korea's charm offensive towards the South could be a sign that it's taking a more conciliatory approach.
But some caution that it could be a tactic to stimulate tensions between Seoul and Washington, and to secure aid and other benefits from its rich southern neighbour.
The optimists believe that diplomacy may finally be given a chance in Beijing.
But that's no guarantee of success.
North Korea believes it's negotiating for the survival of its system - and it sees nuclear weapons as the best and last guarantee of its security.
There's little sign that the Bush administration is ready to make the sort of concessions that would be needed to meet the regime's demands.