The deadline has again been extended for rebel and Sudanese government negotiators, meeting in Nigeria, to sign a deal ending the Darfur conflict.
Rebel groups have misgivings about the AU peace plan
On Sunday, an earlier deadline was extended until Tuesday, in a bid to make reluctant rebels sign the deal.
A new deadline of 48 hours has now been set. It expires on Thursday night.
The US, UK and African Union mediators have been pushing for a deal that could end a conflict that has led to some 200,000 deaths in Darfur.
More than two million people have been displaced by the violence, which started three years ago when black African rebels took up arms against Khartoum.
The Sudanese government and militias backed by it have been accused of committing genocide in their crackdown on the rebels - a charge Khartoum denies.
US Deputy Secretary of State Robert Zoellick, who arrived at the talks in the Nigerian capital, Abuja, on Monday, said: "I believe there has to be an end to this process."
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
An adviser to the African Union said that while the deadline could be extended, the draft agreement could not be re-written drastically.
Alex de Waal said the rebels have to move "from criticising the many injustices that they and their people have suffered to seeing that a much better future can be grasped on the basis of this agreement", Reuters news agency reports.
The Sudanese government says it is prepared to sign, but the rebels say they want further concessions on security, power and wealth-sharing.
The talks between the two parties have been going on for a year.
The original deadline for signing the deal expired on Sunday, prompting a new extension - until Tuesday - and a flurry of diplomatic activity.
The US and UK sent top envoys to the talks in Abuja and US President George W Bush spoke by telephone to his Sudanese counterpart.
According to a White House spokesman, President Bush told President Omar al-Bashir on Tuesday that he must keep up efforts to find a deal on Darfur.
He urged the president to send his envoy, Vice President Osman Taha, back to the talks he had left earlier in apparent frustration at the rebels' stance.
The president also told Mr Bashir he should allow UN peacekeepers, backed by Nato, to take over from an overstretched African Union force in Darfur.
Meanwhile, AU mediator Salim Ahmed Salim urged the black African rebels "to show leadership and make the compromises necessary for peace, for the sake of the people of Darfur".
Reuters news agency quoted a diplomat involved in the mediation as saying that the rebels would be discredited if they rejected the deal.
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 the Justice and Equality Movement (JEM).
The proposed peace deal envisages disarming Janjaweed militia and incorporating rebel fighters into the regular army.
The BBC's Alex Last in Abuja says 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.
The Sudanese government has agreed to the deal
The government is unhappy at this provision, even though it has signed the deal.
But the rebels are also said to be unhappy about arrangements concerning power-sharing and wealth distribution in the vast desert region. They are also reportedly concerned that the peace deal may not be properly implemented.
"The extension of the deadline does not have any meaning for us," said Saifaldin Haroun, spokesman of the main SLM faction, according to the AFP news agency.
"The AU peace proposal does not address our crucial concerns."
Last year, a peace deal was signed with southern rebels which included detailed arrangements on sharing wealth and brought the rebel SPLM into government.
US pressure was instrumental in getting this deal signed.