U.S. and North Korean diplomats acknowledged an irreconcilable deadlock Thursday in long-stalled nuclear disarmament talks, casting doubt on the future of Chinese-sponsored six-party negotiations.

The stalemate, based on the North Korean demand that it be given a light-water nuclear reactor to produce electricity, brought the current round of discussions to a rancorous standstill after three days. Representatives of the participating countries, which also include South Korea, Japan and Russia, did not indicate they would abandon the negotiations, but none outlined a way to keep talks going.

"We're in a bit of a standoff at this point," said Christopher Hill, assistant secretary of state for East Asian and Pacific affairs and chief U.S. negotiator. "We'll have to see where this leads."

If the talks break down permanently, the Bush administration has suggested referring the issue of North Korea's nuclear weapons program to the U.N. Security Council for possible economic and other sanctions. Other participants in the talks, including China, which has veto power on the Security Council, have indicated they would not favor that course. North Korea has warned it would consider such a step tantamount to war.

Chinese diplomats, who sponsor and act as referees in the six-party talks, were meeting with their North Korean counterparts to explore salvaging the discussions.

Hill said he planned to meet with Chinese diplomats on Friday, but he made it clear that neither side seemed ready to budge. "I think it's fair to say we have a rather major disagreement on this point," he said.

A breakdown would represent a major setback for the Beijing government, which since August 2003 has taken a prominent leadership role in seeking a diplomatic solution to one of Asia's most intractable problems. Barring a dramatic turnabout by North Korea's leader, Kim Jong Il, however, it was difficult to see how the gap could be bridged, diplomats said.

"The talks are deadlocked," said the chief Japanese delegate, Kenichiro Sasae. "The differences between positions remain large and there are no prospects of agreement."

A North Korean spokesman, Hyun Hak Bong, said in a statement that his government's demand for a light-water reactor was a litmus test of whether the United States has abandoned hostility toward Pyongyang.

"Providing a light-water reactor is a matter of principle for building trust," the statement said. "The United States says it cannot give us a light-water reactor no matter what. It is telling us to give up the nuclear first without doing its part."

The Bush administration has demanded that North Korea relinquish not only its nuclear weapons program but also its ambition to build a nuclear reactor to produce electricity. Hill said the U.S. government believes that North Korea cannot be trusted on the issue, because it converted a research reactor in the 1990s into a source of weapons-grade plutonium.

Such a plant is out of the question, Hill said, because North Korea expelled U.N. weapons inspectors at the end of 2002 and, in January 2003, withdrew from the nuclear Non-Proliferation Treaty. The nation's energy needs can be supplied by a South Korean-proposed program that is included in the Chinese-drafted plan under discussion here, he added.

North Korean spokesman Hyun Hak Bong, center, said the reactor bid was a test of U.S. acceptance of his government.