Six-nation talks in Beijing aimed at resolving a crisis over North Korea's nuclear programme will continue longer than scheduled, officials say.
Talks are focused on programmes at the Yongbyon nuclear site
China said the talks process was encountering "differences, difficulties and contradictions".
China wants all parties to sign a joint statement as a basis for further talks.
But it remained unclear whether a North Korean offer to stop nuclear activities would be enough to satisfy US demands it completely dismantle its programmes.
The extension of the talks came amid a concerted effort to bridge the gap between North Korea and the US.
China later announced that the talks - originally scheduled to end on Friday - would finish with a ceremony on Saturday morning, according to its state news agency, Xinhua.
China's chief negotiator at the talks, Wang Yi, said the talks process was hitting stumbling blocks, although Chinese government spokesman Liu Jianchao stressed that "gaps between the various parties are gradually narrowing."
The BBC's Charles Scanlon, in Beijing, says China, as the talks' host, is pushing hard for a concrete achievement after six months of hard diplomatic graft.
China wants the parties to agree on a written statement and to sanction more regular meetings at a lower level.
But one draft prepared by China has already been reportedly rejected by the US and Japan because it did not call for a "complete, verifiable and irreversible" end to North Korea's nuclear programmes.
China, US, Russia, Japan, North and South Korea taking part
Set to last until Friday
Saturday session added
Parties sit at hexagonal table, US next to N Korea
On Thursday, North Korea offered to halt its nuclear activities in return for "corresponding measures" by the US, but the Russian chief delegate said Pyongyang wanted to keep that part of its programme meant for "peaceful purposes".
The offer did not appear to extend to a secret enriched uranium project which Washington alleges, but which Pyongyang continues to deny.
Shortly afterwards, Pyongyang called on Washington to give up its "hostile policy" of demanding North Korea scrap all its programmes irreversibly before it gets anything in return.
"The United States is saying that it can only discuss our demands after we give up all nuclear programmes, including for peaceful purposes, as it continues with its stale demand that we give up nuclear programmes first despite our flexible
position," the North Korean embassy said in Beijing.
N Korea wants compensation for freezing nuclear programme
But US says freeze not enough
US wants N Korean uranium programme dismantled
N Korea denies programme exists
Japan wants abductees discussed
N Korea says subject not relevant to nuclear talks
"It is because of this that there has not been a breakthrough in the solution of the problems," it said.
Nevertheless, US Secretary of State Colin Powell was upbeat.
"The results of the first two days of meetings are positive," he told the Senate Budget Committee in Washington.
"There's a promising attitude that is emerging from those meetings and hopefully we can move in the right direction there," he said.
South Korea, Russia and China have offered the North concessions it is demanding in the form of oil aid.
North Korea's economic problems have led to severe energy shortages, which were exacerbated by a US-led decision to suspend shipments of fuel aid to the country.
"The energy aid requires a presumption that North Korea freezes its nuclear activity as a beginning step to dismantle all of its nuclear programs completely, irreversibly and verifiably," South Korea's Lee Soo-hyuck said on Thursday.
A similar deal was struck between the US and impoverished North Korea in 1994 but collapsed after Washington said in October 2002 that Pyongyang had privately admitted to the enriched uranium programme.