Talks in Beijing aimed at ending North Korea's nuclear programme have finished without agreement on a deadline for the country to disable nuclear facilities.
Food and fuel aid has begun heading to North Korea
Negotiators wanted Pyongyang, which has already closed its main nuclear site, to agree a timetable for disclosing and disabling all its nuclear facilities.
But they have now agreed working groups will discuss technical details first.
Envoys from the six countries involved in the talks will meet again in September, Chinese envoy Wu Dawei said.
North Korea pledged to "earnestly implement its commitments to a complete declaration of all nuclear programmes and disablement of all existing nuclear facilities", Mr Wu said in a statement at the end of the talks.
But the deadline that negotiators had hoped for was not in the statement. Instead, the working groups will meet in August to hammer out details of the way forward, he said.
The latest meeting of the two Koreas, the US, China, Japan and Russia marks the end of the first phase of a landmark deal agreed last February.
In the last week, Pyongyang has fulfilled its pledge to shut its main reactor, Yongbyon, and has begun to receive the 50,000 tons of fuel oil it was promised in return.
A total of one million tons of energy aid has been promised to North Korea if it fulfils the second phase by disabling its nuclear facilities and declaring its nuclear secrets.
N KOREA NUCLEAR DEAL
N Korea to "shut down and seal" Yongbyon reactor, then disable all nuclear facilities
In return, will be given 1m tons of heavy fuel oil
N Korea to invite IAEA back to monitor deal
Under earlier 2005 deal, N Korea agreed to end nuclear programme and return to non-proliferation treaty
N Korea's demand for light water reactor to be discussed at "appropriate time"
The BBC's Dan Griffiths in Beijing says that getting this far has been an achievement after four years of talks that often seemed to go nowhere.
But doubts remain over North Korea's commitment to giving up its nuclear arsenal for good, and the challenge now is to keep this process on track, our correspondent adds.
Both US chief negotiator Christopher Hill and his South Korean counterpart Chun Yung-woo sounded an upbeat note as talks concluded.
Mr Hill said he was "still of the view that with a little luck we can wrap this all up by the end of the year, but obviously it's going to be difficult".
"North Korea said it would not drag its feet in moving on to the next phase and would declare everything it has," Mr Chun said. "In that sense, there has been considerable achievement".
But Japan - which has refused to contribute fuel aid until Pyongyang addresses the issue of abducted Japanese citizens - was less positive.
"It was unfortunate that we could not reach a consensus on details," envoy Kenichiro Sasae said.
As well as receiving fuel aid, some 60 trucks from South Korea crossed the border on Friday to make the first delivery of rice aid.
Seoul had promised some 400,000 tons of food aid to the impoverished North as part of the February deal.
The movement of aid follows the shut down of the Yongbyon reactor on Saturday and subsequent closure of four more sites at the complex, all verified by UN nuclear inspectors.
But, despite the optimistic mood, analysts warn of hurdles ahead as the process continues towards complete denuclearisation.
A key stumbling block could be the US allegation that North Korea has a secret uranium enrichment programme. Pyongyang denies this.
Another is that once the second phase of the deal is complete, North Korea - which carried out its first nuclear test in October 2006 - will then have to hand over its nuclear materials.