The African Union has decided to extend its peace mission in Sudan's Darfur region until September at the earliest, before handing control to the UN.
Government supporters are opposed to UN peacekeepers
Sudan is strongly opposed to any switch. Thousands have marched through the capital's streets, threatening "Holy war" against "recolonisation".
Despite the Sudanese objections, the AU agreed "in principle" to ask the UN to take over in Darfur.
More than 2m people have fled their homes in what the US calls "genocide".
Sudan denies backing the Arab "Janjaweed" militia, accused of the worst atrocities in the three-year conflict. It blames the casualties on the black African rebels who took up arms.
The AU's Peace and Security Council met behind closed doors in Addis Ababa to look at a decision which has been delayed since the handover was initially agreed in January.
Afterwards, Ethiopian Foreign Minister Seyoum Mesfin said the AU mission in Sudan would be extended until 30 September.
Correspondents say it would take at least six months for the UN to take control of the peace force, which is expected to be bigger and have a tougher mandate than the AU mission.
The UN has said it would only send a peacekeeping force to Darfur with the permission of the Sudan government.
Sudan's Foreign Minister Lam Akol told the BBC's Newshour programme that the existing force was doing a "good job" and said a UN force could further destabilise the region.
He said the money to be spent on the UN force should instead be used to help the peacekeepers already in Darfur.
But the BBC's Jonah Fisher in Khartoum says that behind the scenes, the government realises that it would be very difficult to reject a UN offer, if it followed a formal request from the AU.
Sudan had threatened to leave the AU if it asked the UN to take over.
Meanwhile, the government of neighbouring Chad has accused the Janjaweed and Sudanese soldiers of stealing hundreds of camels, sheep and cattle in a cross-border raid.
Tension between Chad and Sudan has risen in recent months, with each accusing the other of backing rebel groups.
On Thursday, the US and Nato urged the AU to step down.
"I hope that we can stop the violence and the genocide in Darfur," said US Secretary of State Condoleezza Rice.
UN Humanitarian Relief Coordinator Jan Egeland had expressed frustration with the lack of a decision, warning of "massive loss of life" if there was any further delay.
"We're hanging in by our fingernails and it's slipping in many areas at the moment," he told reporters.
Janjaweed militias were continuing to attack the camps for those displaced by the Darfur conflict, UNHCR spokesman Ron Redmond told the BBC.
The UN refugee agency on Thursday said it was cutting relief work in Darfur because continued violence made it too dangerous for aid workers.
The UNHCR said its 2006 budget for Darfur would be reduced by 44%.
Humanitarian convoys are being targeted, the agency said in its statement released in Geneva, and access to large areas of west Darfur is severely limited, where there are currently over 650,000 internally displaced people.