Salim Ahmed Salim said the talks would continue until midnight on Tuesday, pushing back a scheduled Sunday end to talks that have gone on for two years but so far failed to halt violence behind the deaths of 180,000 people.
Salim, a lead mediator for the 53-nation AU, said the bloc had bowed to requests from the United States and others to continue work on a proposed deal to end fighting.
"The African Union has extended the deadline of the peace talks by 48 hours as requested by the United States and other international partners to allow extensive consultations to go ahead," he told repoters at the talks' site in the Nigerian capital, Abuja.
The African Union, which is mediating the talks to end the conflict behind one of the world's worst humanitarian crises, had set midnight Sunday as the peace conference's end, pressing Darfur's warring parties to sign a peace deal circulated in recent days.
The Sudanese government indicated approval for the draft deal, but rebels said the pact failed to meet their demands for autonomy in the vast western Darfur region or vice-presidential representation in the Khartoum government.
"We are not going to sign it as it is," said Hahmed Hussein, a spokesman for the Justice and Equality Movement, who said in a statement he spoke for both Darfur rebel groups. The other main insurgent group, the Sudan Liberation Movement, earlier asked for more time to consider the document.
For Sudan's war-wracked Darfur region, the only other option to continuing talks is to entirely abandon long-running negotiations meant to end a conflict that has already taken 180,000 lives and left 3 million homeless.
Decades of low-level tribal clashes over land and water in Darfur erupted into large-scale violence in early 2003 when some ethnic groups took up arms, accusing the east African nation's Arab-dominated central government of neglect.
The central government is accused of responding by unleashing Arab tribal militia known as Janjaweed to murder and rape civilians and lay waste to villages. Sudan denies backing the Janjaweed, whom the United States accuses of genocide.
Nearly two years of peace talks have failed to quell the violence and all sides have roundly ignored a cease-fire agreement monitored by 7,000 African Union soldiers on the ground in Darfur, the size of France.
Sudan has indicated it might accept a U.N. force in Darfur if a peace treaty is signed. A beefed-up UN force with a strong mandate is seen as one option to impose peace in Darfur — and calm an African region where violence is on the upswing.
Darfur's violence has spilled into neighboring Chad, where many Darfur refugees are taking shelter, and threatens to escalate. Osama bin Laden last week urged his followers to go to Sudan to fight the proposed U.N. presence.
As talks have continued, the plight of 3 million Darfur refugees has worsened. The U.N. World Food Program said on Friday that it was cutting rations in half for those survivors, citing a lack of funds. The U.N. says the Darfur crisis is among the world's worst humanitarian crises and with the dry season approaching and harvest stores dwindling, Darfurians face even harder times ahead.
International pressure has mounted on Darfur's warring parties in recent days as talks advanced.
In Washington, actors, athletes, politicians and religious leaders rallied Sunday to call attention to the Darfur conflict and urge greater U.S. involvement. More than a dozen rallies were planned in U.S. cities over the weekend.
Meanwhile, U.S. Secretary of State Condoleezza Rice called on China and Russia to join the United States in pushing Sudan to accept U.N. forces.