Individual meetings between envoys from the two Koreas, the US, host China, Japan and Russia took place as the group prepared to resume talks on Tuesday after a gap of more than a year.
The US and North Korean delegates met behind closed doors at the Diaoyutai State Guesthouse in Beijing for more than an hour, the official Xinhua News Agency reported.
The American embassy did not immediately release details of the meeting but earlier US Assistant Secretary of State Christopher Hill said the two sides were "just trying to get acquainted, review how we see things coming up and compare notes".
Referring to Tuesday's talks, he said: "We are looking forward to working hard and trying to make some progress."
He did not say what progress Washington hopes to make.
Hill said on Sunday he did not expect the meetings this week to be the last set of negotiations over demands that the North give up its nuclear programme.
He said the process was "going to take a lot of work".
The talks also include host China, South Korea, Russia and Japan.
Hill said there were likely to be
South Korean Deputy Foreign Minister Song Min-soon and his North Korean counterpart, Kim Kye Gwan, met on Sunday and "agreed to come up with a framework to realise denuclearisation of the Korean Peninsula", a South Korean Foreign Ministry spokesman said.
The last round of talks ended in June 2004 without major progress towards a settlement of the dispute.
It erupted in late 2002 when the United States said North Korea had admitted running a nuclear programme in violation of an earlier agreement.
North Korea says it will drop its nuclear ambitions in exchange for diplomatic relations with the United States and a formal US non-aggression commitment.
It also wants to be removed from Washington's list of terrorism-sponsoring countries, and for economic sanctions against it to be dropped.
Washington has refused to offer concessions until the North is certified free of nuclear weapons, but the North insists on getting something first before abandoning its atomic programme.