The US says fundamental differences remain over North Korea's nuclear weapons programme, at renewed six-nation talks in Beijing.
China hosted a banquet lunch in an attempt to keep the mood convivial
But it says it is trying to draft a list of agreed principles to give new life to the deadlocked diplomacy.
The two sides held a third bilateral meeting on the sidelines of the main talks on Thursday.
Diplomats said the outcome of these bilateral discussions was crucial to the ultimate success of the talks.
Both North Korea and the US have put fresh demands on the table at the talks, which are also being attended by South Korea, Japan, China and Russia.
North Korea wants diplomatic relations with the US and a peace agreement, in addition to the security guarantees and economic help already offered.
It is also demanding the removal of the American nuclear threat to the region.
The US says it is not prepared to discuss issues that relate to its alliances with other countries, and for its part, has called for concessions on North Korea's development of ballistic missiles and its human rights record.
These demands are in addition to Washington's most significant requirement - that Pyongyang agree to the verifiable dismantlement of its nuclear weapons programmes.
The difficulty at this round of talks, as at previous rounds, is the question of sequencing.
North Korea objects to US demands that it make the first move by scrapping its nuclear weapons facilities. Instead it wants a step-by-step process in which it receives progressive rewards and incentives.
The North has also continued to reject American allegations that it is running a secret enriched uranium programme in addition to its well-known plutonium plant at Yongbyon.
That dispute provoked the current crisis, which began nearly three years ago and has blocked diplomatic progress since.
But there has been a more positive atmosphere at this round of talks, says the BBC correspondent Charles Scanlon.
South Korean officials said it was too early to tell whether the prospects for the talks were bright or not, but participants at the meeting said there was a more businesslike mood than at previous meetings.