U.S. Assistant Secretary of State Christopher Hill said Washington cannot accept North Korea's insistence on having atomic reactors for energy.
"In the last few days, it began to emerge that the problem with reaching an agreement was not just the issue of the desire to retain their right to develop commercial -- or so-called peaceful -- [nuclear] energy. But also, they began to insist on a light-water reactor," Hill told journalists.
The negotiators are due to return to talks on 29 August after a break of three weeks. Correspondents say it is unclear how to move forward on the three-year standoff with North Korea -- which has said once again that it is making nuclear weapons.
Hill said there is only one way to move forward. "I hope that they will use this recess time wisely [and] will go back and think hard and long about what to do," he said. "And come back in this same month of August ready to make that decision to do away with its [nuclear] weapons and to reach agreement with the rest of us on the text of this agreement."
But Deputy Foreign Minister Kim Kye-Gwan, the chief negotiator for North Korea, said it is the United States that must reconsider it's position toward the Democratic People's Republic of Korea (DPRK).
"During the recess period, the United States should change their policy saying that the DPRK is not entitled to any nuclear program," Kim said.
Kim said North Korea needs nuclear weapons to protect itself from what it says is the threat of a nuclear attack by the United States. He says North Korea also wants guarantees that there are no nuclear weapons in South Korea.
"Our counterpart requires us to give up the right to have peaceful use of nuclear power. The United States should guarantee it won't attack us with nuclear weapons and provide legal and systematic guarantees. South Korea should get rid of the nuclear umbrella and South Korea should guarantee it has no nuclear weapons and also should guarantee that no nation will provide them with nuclear weapons," Kim said.
The recess of the six-party talks means the meetings have fallen short of the original plan to draft a joint agreement setting out how North Korea would abandon nuclear weapons and what it would get in return.
A Japanese government official says China, Japan, Russia, the United States, and South Korea all have agreed that now is not the time for Pyongyang to insist on the peaceful use of nuclear energy.
"Efforts made by each country should not be wasted. And it is important to bring such efforts to the next stage," Japan's chief negotiator, Kenichiro Sasae, said.
The construction of two light-water nuclear reactors for power-starved North Korea had been part of a 1994 agreement between Pyongyang and the United States.
Under that deal, Pyongyang committed to freezing and eventually dismantling its graphite-moderated nuclear reactors. Those reactors can produce weapons-grade nuclear material more easily than light-water nuclear reactors.
But the project was suspended in October 2003 -- a year after the current crisis began -- when the United States said North Korea had a secret uranium-enrichment program.
The suspension of that project prompted North Korea to withdraw from the Nuclear Nonproliferation Treaty. Pyongyang later confirmed that it has developed nuclear weapons.
(compiled from agency reports)