North Korea has repeated an offer to freeze its nuclear facilities in return for US compensation, ahead of six-nation talks expected next month.
The row centres on North Korea's Yongbyon nuclear plant
But Washington has again insisted a freeze was not enough, suggesting the two sides remain far apart.
China, which will host the talks, has cautioned that resolving the nuclear stand-off will be a slow process.
Talks involving the US, China, Japan, Russia and North and South Korea are due to begin in Beijing on 25 February.
"We demand the United States take corresponding measures in return for a (nuclear) freeze as a first step," said Kim Ryong-song, North Korea's chief negotiator, who is in Seoul for inter-Korean ministerial talks.
"Based on this 'reward-for-freeze' principle, the (nuclear) issue must be settled at the coming six-way talks," he said.
But US State Department spokesman Richard Boucher, speaking on Tuesday, reiterated that a freeze was not enough.
"What we have made clear is that a freeze is not our goal. A freeze is not elimination," he said.
"If they want to talk about a freeze, they can talk about a freeze and we'll see if the discussion leads anywhere," he said.
The US agreed to a North Korean freeze in 1994, an agreement which Washington claims the North did not adhere to.
The substance of any new agreement is not the only sticking point, since the timing of each sides' moves and concessions are also disputed.
The BBC's Seoul correspondent says few analysts expect a breakthrough at the talks.
The new round of talks come after North Korea last month said it had shown its "nuclear deterrent" to an unofficial delegation from the United States.
The US team confirmed they had seen the secret nuclear complex that Washington believes is being used to develop nuclear weapons.
They were the first group from outside North Korea to visit the Yongbyon facility since the North forced UN inspectors to leave at the end of 2002.
In 1994, North Korea agreed to halt activities at Yongbyon, 90 kilometres (50 miles) north of the capital, Pyongyang, under a deal with the United States.
But after that agreement broke down in late 2002, North Korea claimed to have finished reprocessing 8,000 spent fuel rods being stored at Yongbyon - enough to help it build up to six more nuclear weapons.
The stand-off was triggered when the US said Pyongyang had admitted to harbouring a separate, enriched uranium programme.