After 13 days of arduous negotiations, diplomats at six-nation talks on North Korean nuclear disarmament acknowledged Sunday that they had reached a deadlock and would return home without agreement on how to revive long-stalled efforts to create a nuclear-free Korean Peninsula.

China, which hosts the talks, announced that the negotiations would resume during the week of Aug. 29. Wu Dawei, the Chinese delegation chief, acknowledged at a news conference that profound discord had prevented agreement on the basic disarmament principles that were the goal of this round of talks. But he portrayed the decision to pick up the talks again after three weeks of recess as a demonstration of resolve by all six nations to overcome their disagreements.

"The agreement reached among the six parties to resume negotiations shows we do not fear these differences," he declared.

The stalemate nevertheless marked a dramatic setback for the six-party negotiating process, begun in August 2003 under Chinese sponsorship as a way to peacefully resolve the crisis over North Korea's nuclear weapons program. This round of talks, the fourth, had been hailed as a new departure that ended a 13-month boycott by North Korea and was characterized by increased flexibility and resolve from Washington and Pyongyang to move forward.

But the discussions, billed as a search for "agreed principles" to underpin further negotiations, quickly bogged down over the same fundamental differences between North Korea and the United States that had prevented agreement during the three previous rounds. These included North Korea's demand to retain nuclear plants to produce energy for peaceful purposes, its insistence that U.S. nuclear protection for South Korea be part of the negotiations, and discord over when the dismantling of North Korea's weapons program should occur in relation to the economic aid and diplomatic recognition it would receive in return.

Chinese and other officials said the fact that all six delegations continued their discussions so long represented progress. Moreover, U.S. and other diplomats said the differences over North's nuclear program had been shortened considerably.

Nevertheless, failure to sign a document listing the principles for further negotiations was seen as a blow to China's status as sponsor of the talks. The sponsorship has been a major diplomatic initiative for the Beijing government, which had earned praise from the Bush administration and others for using its rising regional influence in a constructive manner. As North Korea's neighbor and major ally, China played a decisive role in coaxing North Korea back to the table.

At the same time, some U.S. officials have criticized the Chinese leadership for refusing to exert more pressure on North Korea to end its nuclear weapons program. For instance, China turned down a U.S. request earlier this year to reduce the flow of oil to North Korea as a way to induce the Pyongyang government to give up its nuclear ambitions and return to the talks.

Christopher Hill, assistant secretary of state for East Asian and Pacific affairs and the head of the U.S. delegation, emphasized that the United States also was eager to keep the talks alive despite the setback in this round. "This is not easy, but I can assure you the U.S. government is very interested in reaching an agreement," he told reporters Saturday.

Some senior Bush administration officials have suggested, however, that the negotiations have little chance of success and that the best course is to refer the issue to the U.N. Security Council for sanctions on North Korea.