A deadline for warring factions in Sudan's Darfur region passed with last-minute attempts to reach a deal.
Negotiations in Abuja have gone right to the wire
Talks involving rebel factions and African mediators continued hours after a midnight (2300 GMT) deadline, which has already been extended twice.
However, the smallest rebel group said it would not sign the document.
The Justice and Equality Movement (JEM) want rebels to have the vice-president post and for Darfur to have a greater share of Sudan's wealth.
"We said that unless fundamental changes are made to this document, it's extremely difficult for us to sign it," Jem negotiator, Ahmed Tugod, told Reuters news agency.
It was not immediately clear what effect this would have on the negotiations, which international negotiators say represents the best opportunity for peace in Darfur.
US and UK envoys have been urging an agreement.
The UK's International Development Secretary, Hilary Benn, said he and US Deputy Secretary of State Robert Zoellick were working hard to broker a deal.
"We've listened carefully to the points, in particular, that have been put to us by the movements because, of course, currently they are saying they are not able to sign the agreement.
"But what we're stressing to everyone we're talking to is: this is the moment, this is the best opportunity and the people of Darfur need this agreement more than anyone else."
Nigerian President Olesegun Obasanjo and Republic of Congo President Denis Sassou Nguesso, the AU chairman, have been holding a series of last minute meetings to try to reach a deal.
But the BBC's Alex Last, who is at the talks in Abuja, says there has been no indication whether or not an agreement might be accepted.
Sudan's government has appeared willing to sign the peace plan, but rebels want more security and power-sharing concessions.
Our correspondent says the rebel leaders face losing international support and sympathy.
If no agreement is signed the Sudanese government would be in a much stronger diplomatic position in relation to the Darfur conflict, and the wider region could be further destabilised, he adds.
DARFUR DRAFT PEACE PLAN
Pro-government Janjaweed militia to be disarmed
Rebel fighters to be incorporated into army
One-off transfer of $300m to Darfur
$200m a year for the region thereafter
Having already extended the deadline for an agreement, there appears little chance that the African Union is ready to stretch Thursday's deadline much further.
More than two million people have been displaced by the violence and some 200,000 people have died since the conflict began three years ago when black African rebels took up arms against Khartoum.
The Arab-dominated government responded with a scorched earth policy and pro-government Janjaweed militias have been accused of committing genocide in their crackdown on the rebels - a charge Khartoum denies.
Four parties are at the talks in Abuja: the Sudanese government, the pro-government Arab Janjaweed militias, and two rebel groups - the Sudanese Liberation Movement (SLM) and Jem.
Mediators hope that the proposed deal can be amended to increase the number of rebels integrated into the army, while dropping the provision that the Janjaweed disarm before the rebels.