Vice Foreign Minister Kim Kye Gwan said "differences in opinions" remained between the North and the United States.
"Our decision is to give up nuclear weapons and programs related to nuclear weapons if the United States removes its nuclear threat against us and when trust is built," Kim said outside the North Korean Embassy in Beijing.
The North has alleged the United States has nuclear weapons in South Korea, a claim both Seoul and Washington deny. However, the North could also be referring to other American forces across the region, where the US military has maintained a strong presence since the end of World War II.
No plans to invade N Korea: US
Despite the disagreements, Kim said the North still looked to "narrow these differences as much as we can to present results."
Top envoys from all six countries on Tuesday discussed a draft of a proposed statement of principles as they struggled with North Korea's demands for what it should receive if it disarms.
"There are five parties that are in pretty close agreement on those principles and the key question is whether North Korea is willing to make the strategic decision it needs to make to go forward," US Deputy Secretary of State Robert Zoellick said in Beijing, where he was on a visit separate from the nuclear talks.
As a result of the latest meeting, China proposed a new draft "that reflects a balance" of what was discussed, South Korean Deputy Foreign Minister Song Min-soon said Tuesday evening. He said meetings would continue Wednesday on the proposal.
Delegates at the talks expressed frustration over the lack of progress earlier Tuesday before heading into the first meeting of all head delegates since Saturday.
Japanese
"I can't say discussions on the wording of the agreement are going smoothly," Machimura said. "North Korea continues to deny that it has a uranium enrichment program."
US officials said in late 2002 that the North admitted to violating a 1994 deal by embarking on a secret uranium enrichment program, sparking the latest nuclear standoff.
"I don't know where we go with this," the chief US delegate, Assistant Secretary of State Christopher Hill, said before Tuesday's meetings.
His South Korean counterpart, Song, added: "In the current situation, we are almost running out of wisdom."
Unlike previous negotiations where the sides failed to agree on a joint statement, delegates this time have set no deadline for the talks and appeared determined to work out a declaration.
No details of any drafts have been released, but reports have said it would mention energy aid and a security guarantee for Pyongyang and eventually normalized political relations with Washington.
"We'll stay here as long as we feel we're making progress," Hill said late Monday. "If we're not making progress, we're not going to stay."
Despite delegates' pessimistic tone, analysts cautioned it was too soon to talk about deadlock.
"North Korea has a tendency to use brinkmanship in the last stage to get maximum concessions," said Ko Yu-hwan, professor of North Korean studies at South Korea's Dongguk University.
"The pessimistic atmosphere or last-minute struggle can, in a way, be seen as a sign that we are close to getting results from the talks."
North Korea claims nuclear weapons
In February, the North claimed it had nuclear weapons and has since has claimed it has taken steps that would allow it to harvest more plutonium for possible use in bombs.
Many experts believe the North already has enough weapons-grade material for about a half-dozen atomic weapons.