The top US nuclear negotiator Christopher Hill has had a meeting in Beijing with his North Korean counterpart, Kim Kye-gwan.
Mr Hill said an understanding had not yet been reached
The meeting was the first since North Korea missed a year-end deadline to submit a detailed declaration of its nuclear facilities.
Pyongyang has pledged to bring an end to its nuclear programme in return for aid and diplomatic concessions.
But Mr Hill said there was more work to be done to secure an understanding.
Assistant Secretary of State Mr Hill is on a tour of the East Asia region prior to a visit by US Secretary of State Condoleezza Rice next week.
His unannounced visit to Beijing, which is hosting the six-party talks on North Korea's nuclear disarmament, was aimed at restarting negotiations following January's setback.
South Korea's state media said Tuesday's meeting was "seen to bode well" for the talks and was "viewed as reflecting Pyongyang's will to continue dialogue".
As he left Beijing, Mr Hill told reporters he had had "a good, substantial discussion" with Mr Kim.
FEBRUARY 2007 DEAL
N Korea to "shut down and seal" Yongbyon reactor, then disable all nuclear facilities
In return, it will be given 1m tonnes of heavy fuel oil
Under an earlier 2005 deal, N Korea agreed to end nuclear programme and return to non-proliferation treaty
N Korea's demand for a light water reactor to be discussed at an "appropriate time"
"We discussed ideas that China had had and how things could be moved," he said.
"I think (North Korea) understand our point of view, but we won't have a complete and correct declaration until we have a complete and correct declaration."
"So I am not sure we yet have an understanding on that."
North Korea wants to be removed from the list of countries which the US claims supports terrorism, but Washington have said this is dependant on the declaration.
Pyongyang had promised to submit the declaration - including details of a suspected uranium enrichment programme - by the end of 2007 but it failed to do so.
There are also signs that the process of removing fuel rods from the Yongbyon reactor had slowed down recently, following Pyongyang's complaints that US aid was not arriving fast enough.
The disabling of the reactor was the first stage of the aid for disarmament deal.
Meanwhile North Korea has accused Japan, one of the six states involved in the negotiations, of attempting to "convert the multinational talks into a platform for confrontation".
State media reported a cabinet paper as saying Japan wanted to "scuttle the... talks in case everything goes against its will".
Japan has not responded.