A midnight deadline for parties involved in the Darfur conflict to reach a peace agreement has passed, with no sign of a deal being reached.
The rebels have been fighting the government since 2003
African Union mediators later extended the deadline for another 48 hours.
The small Justice and Equality Movement (Jem) and a faction of the main group, the Sudan Liberation Army (SLA), have rejected the deal as it stands.
The rebels as a whole have not reached a decision at the talks in Nigeria. The Khartoum government has agreed to sign.
The conflict has killed 200,000 and driven two million from their homes.
Jem spokesman Ahmed Hussein told the BBC the peace plan put forward by the African Union failed to address his group's "minimum demands" and favoured the Khartoum government.
One of the factions of the Sudan Liberation Army (SLA) made an equally uncompromising statement. "If the proposal does not include all our demands we will not sign," its spokesman said.
However the chief negotiator of the SLA left the possibility open that a deal could be reached.
The BBC's Alex Last in Abuja, where the talks are being held, says that if the SLA mainstream can be brought on board, others are likely to follow.
Mr Pronk has said the peace plan had been the result of months of arduous negotiation and was not up for renegotiation.
However he suggested that the midnight deadline set by the AU did not matter as long as the rebels signed within a day or so.
The plan calls for pro-government Arab militias to be disarmed, and rebels fighters to be merged into Sudan's forces.
The 85-page draft also aims to end what Darfur rebels say is long-standing neglect of the province by the Khartoum government.
About two million people have been left homeless in Darfur
It calls for a one-off transfer of $300m to Darfur, with $200m a year for the region thereafter.
The rebel groups have been holding a series of meetings with the mediators and each other to work out a common position.
Some rebel leaders are reportedly demanding the Sudanese vice-presidency.
There are also concerns over the demand for rebel forces to lay down their arms before they are integrated into the Sudanese army.
The Khartoum government announced its acceptance of the peace plan on Sunday.
"The government... wishes to confirm its decision to formally accept this document and its readiness to sign it," it said.
As negotiators sought to secure a deal, campaigners held a series of mass rallies across the United States calling for an end to the conflict.
Speakers in Washington included the actor George Clooney, who described Darfur as "the first genocide of the twenty-first century".
"We're at the doorstep of something we thought was impossible to dream of in the twenty-first century," he said.
"If we turn our heads and look away and hope that it'll all disappear, then it will. All of them, an entire generation of people."
The United Nations' top human rights official, Louise Arbour, meanwhile, began a six-day visit to Sudan, with a visit to Darfur scheduled for Monday.
The AU - which has 7,000 peacekeepers in Darfur - has struggled to stop the violence between the rebels and the government-backed Janjaweed militias.
The conflict began in early 2003, when rebel groups began attacking government targets.
Our correspondent says even if the peace deal is finally signed, the next test will be to see if its actually implemented on the ground.