US President George W Bush has authorised $25m (£13m) in fuel aid to North Korea under an agreement aimed at ending the country's nuclear programme.
The US, China, two Koreas, Japan and Russia are meeting in Beijing
Under a February deal, the US and other participants at the six-party talks agreed to provide North Korea with aid.
In return North Korea said it would shut down its main nuclear reactor - which it did in July - and eventually dismantle its entire nuclear programme.
Envoys are meeting in China to pin down details of the second part of the deal.
The announcement by the US followed the first day of negotiations in Beijing between the two Koreas, China, Japan, Russia and the US.
Heading into the talks on Thursday, US Assistant Secretary of State Christopher Hill told journalists that the idea was "to lay out a road map until the end of the year".
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"
He said that North Korea had agreed to some measures but more work was needed.
"[North Korea] has agreed to some steps and I think we've looked at what they've agreed to and, frankly, we'd like more and they'd like less and let's see what we end up with," he said.
There was no agreement on what constituted disabling yet, he said.
The South Korean negotiator, Chun Yung-woo, said that the differences were not insurmountable because the "political will" was there to reach an agreement.
North Korea tested its first nuclear device in October 2006.