North Korea's unexpected insistence that it still has the right to build light-water reactors to generate electricity became the main deal breaker during 13 days of sometimes acrimonious and ultimately unsuccessful discussions on eliminating nuclear weapons on the Korean Peninsula, the chief U.S. negotiator said Sunday.

The goal during a three-week recess called by China will be to encourage senior North Korean leaders to make a strategic decision to forgo and dismantle all nuclear capacity in return for recognition and economic aid, said the diplomat, Christopher Hill, assistant secretary of state for East Asian and Pacific affairs.

"One gets the impression there are some people back in Pyongyang who still have not dragged themselves over the line to be ready to give this up," Hill told reporters as he prepared to return to Washington empty-handed.

Despite the prolonged negotiations, the six nations represented here failed to reach agreement on a set of principles that would serve as the basis for more detailed talks. They resolved, however, to return for more negotiations the week of Aug. 29, after what Chinese officials described as a period during which diplomats can consult with their governments.

"This is the consensus of the six parties," said the chief Chinese negotiator, Deputy Foreign Minister Wu Dawei, in announcing the three-week break in negotiations. China is the host and sponsor of the talks, which began in August 2003 and include the United States, North and South Korea, Japan and Russia, as well as China.

The failure to reach agreement despite 13 days of negotiations marked a particular setback for China, which has earned praise for taking the lead in trying to resolve a difficult crisis in which the United States and North Korea are the main protagonists. Wu voiced determination to press on and expressed hope that an agreement will eventually be reached despite the disappointment in this round.

The chief North Korean delegate, Deputy Foreign Minister Kim Gye Gwan, insisted that his country retain the right to operate nuclear reactors for electricity production as part of any agreement. "What we are making is a just demand," he told reporters after the talks broke up.

Kim did not say what kind of reactor North Korea was demanding, but Hill said that in the closed negotiations Kim was insisting on a guarantee for a light-water reactor.

The United States has said that North Korea should not even be allowed to maintain reactors for civilian use because it turned a research facility at Yongbyon, near the capital, into a production center for weapons-grade plutonium after the collapse of a 1994 agreement restricting nuclear activity. Going a step further, North Korea announced in February that it has used the material to make nuclear weapons.

Light-water reactors are considered less likely than plutonium reactors to be a potential source of weapons-grade material, but U.S. officials still have nuclear proliferation concerns about such installations.

Diplomats at the current round of talks suggested that there could be room for compromise on the civilian nuclear energy question if North Korea again accepts international nuclear nonproliferation controls. But none of the other five nations represented here was willing to issue a guarantee for a light-water reactor, according to a senior U.S. official who participated in the talks.

The Bush administration maintains North Korea also has developed a secret program to produce weapons-making material from highly enriched uranium. Without acknowledging that such a program exists, the official said, North Korean diplomats here agreed the highly enriched uranium dispute must be addressed. Previously, North Korean officials had dismissed the U.S. allegation.