Sudanese protest leaders told AFP Friday talks with the country's army rulers have been postponed, just days after the two sides signed a power sharing deal.
"The talks have been postponed," said prominent protest leader Omar al-Digeir.
"We need more internal consultation to reach a united vision," he added, with no new date set for negotiations to resume.
Another protest leader, Siddig Youssef, also confirmed the talks had been suspended.
On Wednesday, the two sides initialled a "Political Declaration" that aims to form a joint civilian-military ruling body, which in turn would install an overall transitional civilian administration for a period of 39 months.
At Friday's talks the two sides were to finalise a "Constitutional Declaration" to thrash out crucial remaining issues.
They include whether to give immunity to generals accused of being behind violence against protesters, the formation of a transitional parliament and the role of paramilitaries.
However, protest leaders said that the three rebel groups that are part of the umbrella protest movement had expressed reservations over Wednesday's deal.
"I'm going to Addis Ababa to meet the Sudan Revolutionary Front to get their opinion," Digeir said, referring to the rebel groups currently based in Ethiopia.
"They are not happy with" the agreement signed with army leaders, Youssef said.
The groups had been fighting government forces for years in the war-torn regions of Darfur, Blue Nile and South Kordofan.
Sources close to negotiations told AFP that these groups have demanded that the "Constitutional Declaration" specify that peace negotiations in the three conflict zones would be a top priority for the new transitional government.
Once such a peace deal is finalised, sources said the rebel groups want their representatives to be part of the transitional government.
They also called for the extradition from Sudan of those accused by the Hague-based International Criminal Court of a litany of crimes, including ousted leader Omar al-Bashir.