U.S. Deputy Secretary of State Robert B. Zoellick delivered a stern message Tuesday to squabbling anti-government rebel groups from Sudan's conflicted Darfur region, saying they must unify or lose international sympathy and risk a return to war.

"My message was, 'Look, at some point you have to take responsibility for your own people,' " Zoellick told reporters on his plane to the Sudanese capital from Nairobi, where he met with the rebel leaders. " 'While you are bickering, people are dying.' "

Zoellick's words capped a dramatic and awkward day of talks with two feuding factions of the Sudan Liberation Movement (SLM). The group launched a rebellion in 2003 against the central government in Khartoum, accusing it of monopolizing wealth and power.

But now the rebels are fighting among themselves, and that has undermined peace talks, which are to begin their seventh round in Abuja, the capital of Nigeria, on Nov. 20.

Tuesday began in confusion when several leaders of both factions each claimed to be official leaders of the SLM in talks with Zoellick, held at Nairobi's Safari Park Hotel. They shook hands, and posed for press photos. Then they glared at each other and stormed out, huddling afterward in separate corners.

Zoellick was left alone. Visibly annoyed, he sat down and reviewed his notes.

"I'm the historic and present leader," Mohamed al-Nur, a founder of the SLM, said outside the meeting room. "I can't sit with the others who say they are the SLM."

"Let him sit as a member, not as a leader," said Saif Haroun, a spokesman for Minni Arko Minnawi, the newly proclaimed leader.

Minnawi had said he would attend, but did not show up. Instead, he spoke to Zoellick by phone. Haroun said Minnawi was too busy cementing his power to leave Sudan, but he did send an entourage of negotiators.

The bizarre diplomatic moment reflected the tough reality of making peace in a conflict in which getting even one side to the negotiating table is fraught with complications.

Rights groups and the United Nations have largely blamed the Khartoum government and its allied Arab militiamen known as Janjaweed for the burning and bombing of villages. But recently, non-Arab rebels have also been blamed for kidnapping aid workers and hijacking food convoys.

While Zoellick was flipping through his notes, he told his aides to tell the rebels, "I've come all this way, and I am prepared to sit in this room. If you don't want to come back in, I will draw my own conclusions that you don't want my help."

After 30 minutes, the rebels re-entered the room. But at first they said they would not talk to each other.

Calling himself "the historical and legitimate leader," al-Nur said he had been unseated at a Darfur conference last week. He boycotted the conference and said it did not fairly represent all the tribes in Darfur.

Meanwhile Minnawi, another guerrilla fighter, said he had been elected president at the conference and was the rightful leader. The two men come from rival tribes, but theirs is also a struggle of personalities and power, analysts said. "In the worst-case scenario, the SLA could end up fighting each other," said Hafiz Mohamed, Darfur program coordinator with Justice Africa, a London-based research group, who attended the meeting. Zoellick said just getting the men in the room to talk meant that the meetings were valuable. In statements later that evening, both rebel factions sounded more conciliatory.

But officials from the African Union, which is hosting the peace talks, said the proof would be how the rebel factions behave there.

"Liberation movements have a habit of splitting and forgetting about the ordinary people they were liberating," said Abdel Mohammed, part of the mediation team for the African Union. "It's like history repeating itself. It's very worrying."