Three previous rounds of talks failed to end the crisis, and negotiators from the two Koreas, the United States, Japan, Russia and host nation China -- meeting for the fourth time in two years – are facing the prospect of another abortive outcome.
A fourth round without agreement would call the entire talks process into question -- an outcome which could tempt Washington to take the issue to the UN Security Council.
That option has been opposed by Pyongyang's closest ally, China, which has much at stake as host of the six-party talks, and by North Korea, which has denounced the possibility of UN sanctions as tantamount to war.
Weary envoys to the marathon talks held bilateral contacts; but all eyes were on Pyongyang's delegation, which continued to refuse to sign up to even the barest statement of principle. Chinese officials have put forward four drafts to no avail.
"Everyone knows the score right now," top US negotiator Christopher Hill told reporters. "We are waiting for North Korea to give an answer to the Chinese draft and they know exactly what the situation is."
"We are waiting for North Korea to give an answer to the Chinese draft and they know exactly what the situation is"
Top US negotiator at the six-party talks
Hill added: "We really need clarity on the principles, it is precisely the clarity that we are seeking. That is so necessary.
"Everyone in Washington very much wants to see we reach an agreement, an agreement on principles, so that we can move on."
With no end-date set, Hill said he would stay in Beijing "as long as I feel it is useful to be here."
A Japanese delegation source said the talks were likely to continue into the weekend.
Looking to China
Both Hill and Japanese chief delegate Kenichiro Sasae were consulting the Chinese to seek a way out of the impasse.
"I'm going to meet the Chinese; but much depends on whether North Korea is ready to make an important decision," Sasae told reporters.
Russia's chief negotiator and deputy foreign minister, Alexander Alexeyev, returned to Beijing on Thursday to resume taking part in the talks. Deputies had been handling negotiations since he left for Moscow on July 30.
China is expected to prevail upon
the North Koreans to fall in line
"We will try our best to make the talks success," Xinhua news agency quoted Alexeyev as saying. He expected the talks to last one to two more days.
Intelligence experts estimate the North Koreans have stockpiled enough plutonium for up to nine nuclear weapons.
Pyongyang is demanding energy aid, security guarantees and diplomatic recognition in return for scrapping its nuclear programmes. Washington has insisted the programmes are jettisoned before the concessions flow.
Top South Korean envoy Song Min-soon said the latest Chinese draft statement contained points on the North's dismantling of the programmes and matching measures by the other parties.