North and south Sudan have agreed to withdraw all unauthorised forces from the contested Abyei border region, the United Nations said, in an attempt to defuse tensions in the oil-producing flashpoint.

The south, where most follow Christian and traditional beliefs, overwhelmingly voted to declare independence from the mostly Muslim north in a referendum in January.

But both sides claim Abyei and have built up forces, beyond an agreed joint north-south unit, in the remote area. Analysts say Abyei is one of the likeliest places for conflict to erupt before the south secedes on July 9.

The pullout of all unauthorised forces would start on Tuesday and be completed within a week, the United Nations Mission in Sudan (UNMIS) said in a statement late on Sunday after a meeting of the joint forces from north and south in Abeyi.

"There was goodwill on both sides and we hope to follow up on this spirit, to see that it is actualised, because Abyei is very important in the peace process," UNMIS Force Commander Major General Moses Bisong Obi said in the statement.

Last week, at least 14 people were killed in clashes between northern and southern forces in Abyei, according to the UN Both sides blamed each other for starting the violence.

Only a unit of joint forces comprising police and army from north and south, working with UN forces, is allowed in Abyei, straddling north and south to ensure stability.

But both sides have built up troops and heavy weapons around the underdeveloped region, according to satellite images and the United Nations.

Last month, Sudan's President Omar Hassan al-Bashir said he would not recognise south Sudan as an independent state unless it gave up a claim on Abyei, made in the south's draft constitution.

Sudan's north and south have fought for all but a few years since 1955 over oil, ethnicity, religion and ideology. The conflict, which ended with a 2005 peace deal, killed an estimated two-million people and destabilised much of east Africa.

Abyei residents were also supposed to have a referendum in January over whether to join the north or south. But disputes over who could vote derailed that ballot and talks over the status of the region have stalled.

Northern and southern leaders have also made little progress in talks over a range of issues including how they will divide up debts and assets, and how the south might pay the north to transport oil after the split.