The government of Sudan and the main rebel faction signed a peace agreement Friday, marking a step forward in an internationally backed effort to end conflict in the western Darfur region.

Though two smaller rebel groups maintained their rejection of the treaty, U.S. Deputy State Secretary Robert Zoellick indicated they could be bypassed.

"Today the largest group, Minni Minnawi's, has agreed to sign and the government of Sudan (has) agreed to sign as well," Zoellick told The Associated Press earlier. "Not all the movements are in accord, but we're already getting phone calls that people with (rebel faction leader) Abdel Wahid (Nur) believe he has made a mistake."

The breakthrough in the deadlock came when Sudanese Liberation Movement faction leader returned to the talks, following a late-night session.

Among those taking part in the talks were two top Canadian diplomats, the high commissioner for Nigeria, David Angell, and United Nations Ambassador Allan Rock.

The Canadians met directly with rebel leaders to identify their hold-out positions and try to work them through.

"The intense pressure by the international partners on the rebels and on the government was decisive," Rock told CP.

The peace deal calls for a ceasefire; disarmament of pro-government militias accused of some of the war's worst atrocities; the integration of rebel fighters into Sudan's armed forces; protection for civilians; guarantees that rebel factions would have the majority in Darfur's three state legislatures.

However, the rebels did not get the national vice-presidency they had been holding out for.

The other factions had been demanding for a vice-president's spot as opposed to a top presidential adviser from Darfur.

The faction led by Nur, who founded the Sudanese Liberation Movement that launched the revolt against the government but has since splintered, abandoned the talks before dawn Friday.

Another rebel group, the Justice and Equality Movement, also rejected the accord.

"Unfortunately, the draft does not fulfill the ambitions of the people of Darfur," JEM negotiator Ahmed Tugod told the Arab satellite TV station Al-Arabiya. "This deal cannot produce logical results that lead to solving the Darfur issue. We are against partial solutions."

Further complicating the issue, one of Nur's top negotiators, Abdulrahman Moussa, said he was creating his own Front for Liberation and Renaissance and taking half of Nur's camp with him to support the peace accord.

Nur "is not compromising and I don't think he is seeking peace, especially after the generous offer from Zoellick," Moussa said.

Sudan's government stayed out of the talks as it had already agreed days ago to an initial proposal drafted by AU mediators.

Decades of low-level tribal clashes over land and water in Darfur erupted into large-scale violence in early 2003.

The rebels took up arms, accusing the government of discriminating against the black residents of Darfur.

The government is accused of responding by unleashing Janjaweed militias, who are blamed for the worst atrocities such as mass killing and rape, but it's a charge Sudan denies.