The US chief negotiator on North Korea's nuclear programme says he has come to this week's six-nation talks in the spirit of making real progress.
N Korea blamed US aggression for the suspension of talks
Christopher Hill was speaking on his arrival in China for the latest round of negotiations.
The talks, aimed at persuading North Korea to stop developing nuclear weapons, begin in Beijing on Tuesday.
Earlier, Chinese state media reported that officials from North and South Korea had held a preliminary meeting.
North Korea agreed to resume the six-nation talks earlier this month, more than a year after it suspended them, blaming US aggression.
Russia, China and Japan are also involved in the discussions.
Mr Hill said he was deeply committed to the talks.
"I wouldn't expect this to be the last set of negotiations ... we would like to make some measurable progress, progress we can build on for a subsequent round of negotiations," he said.
"We come here in a real spirit of trying to make some real progress."
South Korean Deputy Foreign Minister Song Min-soon echoed the comments after meeting his northern counterpart.
"We shared the view that participants in the talks should produce substantial progress and come up with a framework for the realisation of a nuclear-free Korean peninsula," Yonhap news agency quoted him as saying.
Pyongyang has been making calls for a peace treaty with the US in the days leading up to the talks.
But Washington has been refusing to talk about any kind of pact until North Korea agrees to shut down its nuclear weapons programme.
The US has indicated that the country could face further sanctions if it fails to resolve the nuclear crisis, although it has stressed that it does not intend to attack the North.