Obasanjo is the current chairman of the African Union (AU) and the Nigerian government is hosting peace talks in Abuja between the rebels and the Sudanese government on behalf of the continental body.

An AU statement on Friday said Obasanjo had personally intervened on Thursday as “part of ongoing efforts to move forward” the negotiations.

The latest round of Darfur peace talks began on 10 June, but have so far achieved very little. Mediators say that the parties are painstakingly inching their way towards a declaration of principles, but they warn that infighting within the two rebel groups could make any peace document meaningless.

Officials in the mediation team say the leadership of the Sudanese Liberation Army (SLA), the bigger of the two rebel groups, has split, with some members declaring allegiance to president Abdel Wahed Mohamed al-Nur and others rallying around the secretary general, Minni Minnawi.

Both men arrived in Abuja three weeks ago for the relaunch of the Darfur peace talks, which had been on ice for six months, but Minnawi left soon afterwards.

Minnawi's supporters, who say they command the greater fighting force in Darfur, subsequently denounced Nur, the current head of the SLA negotiating team in Abuja, declaring that he no longer represented them. They said they would not be bound by any deal that he agrees in Nigeria.

Similar infighting has plagued the smaller rebel group, the Justice and Equality Movement (JEM).

A group claiming to represent JEM's field commanders has rejected the leadership of Khalil Ibrahim. One of the field commanders, Mohamed Salih Hamid is in Abuja, but has not been allowed to join the talks.

“We can’t accept any changes to representations now," one AU mediator told IRIN on Friday. "We have to stick to the people we’ve been dealing with all along.”

AU mediators, led by Salim Ahmed Salim, a former Tanzanian foreign minister, are battling to try to hammer out a deal that would end the war in Darfur, which erupted in February 2003.

The conflict pits Sudanese government troops and Arab militias against rebels fighting to end what they call the neglect and oppression of the inhabitants of Darfur, a semi-desert region the size of France.

The United Nations has described the situation in Darfur as the world’s worst humanitarian crisis. It estimates that 180,000 lives have been lost and that a further two million have been people forced to flee their homes.

Talks between Khartoum, the SLA and JEM stalled in December amid allegations of ceasefire violations by all sides.

AU mediators managed to get the parties back to the negotiating table last month after much behind-the-scenes wrangling.

However, the restarted talks ran into bickering almost immediately over whether representatives from Chad and Eritrea should be allowed to attend.

JEM accuses Chad of supporting Khartoum, while the Sudanese government delegation alleged that Eritrea was the main backer of the rebels.

AU mediators have not yet dealt decisively with these complaints, opting instead to hold one-on-one sessions. They have managed to persuade the parties to study and evaluate a draft document stipulating the terms for sharing wealth and power between the central government in Khartoum and Darfur's six million inhabitants.

But things are moving at a snail's pace.

Meanhwile, Nigeria on Friday began deploying the first batch of a 2,000-strong reinforcement of AU troops to Darfur.

AU leaders, who voted for the increase in April, hope that the extra personnel will transform the small ceasefire monitoring force that exists at present into a larger force capable of protecting unarmed civilians from attack.

The first contingent of 142 Nigerian soldiers was airlifted to Darfur from a military base in the northern city of Kaduna on Friday.

Nigerian military spokesman Brigadier-General Ganiyu Adewale said 500 more soldiers would be flown out next week to complete the deployment of a full battalion.

“Another battalion (680 troops) will leave in August, with the last one joining them later,” said Adewale.

The Nigerian soldiers form part of 5,300 new troops that are expected to raise the strength of the AU force in Darfur to 7,700.