Delegates at talks in Nigeria said on Friday that rival rebel factions, whose arguments hampered six previous rounds of talks, have negotiated jointly during the current round, but new signs of disunity have come out into the open.
Noureddine Mezni, a spokesman for the African Union (AU) mediation team, said: "We cannot continue to negotiate forever. Divisions in the [rebel] movements complicate the whole process and we are trying to bring the factions closer together."
The AU, which has about 7,000 peacekeepers in Darfur where violence is growing, says it is hopeful that a deal will be reached, but it is sending increasingly strong signals that its patience with the Abuja negotiators is limited.
Salim Ahmed Salim, the AU special envoy for the Darfur conflict, told the UN Security Council last month that it should consider "carefully targeted sanctions" against those who delay progress towards a settlement.
Delegates from the two rebel movements, the Sudan Liberation Army (SLA) and the smaller Justice and Equality Movement (JEM), said they felt that a peace deal could be achieved. However, rival factions accused each other of undermining the talks.
The SLA and the JEM took up arms in early 2003 over what they describe as marginalisation by Khartoum. The government backed proxy militias to fight the rebels and the conflict has killed tens of thousands of people and driven more than two million from their homes.
The UN Security Council is calling for early contingency planning for a UN peacekeeping mission to replace the AU contingent in Darfur.