By Martin Plaut
BBC Africa analyst
For days now the United Nations has nervously monitored the planeloads of Sudanese troops arriving in North Darfur.
Now the purpose of the build-up has become clear: the African Union is being asked to leave, and the days of international peacekeeping are to end.
The AU force has been under-equipped
Khartoum is to settle the three-year-old rebellion on military terms.
There now seems no way that a United Nations force can be deployed in Darfur, since the idea of peacekeepers fighting their way into this vast, remote region is hardly plausible.
That will leave the huge camps housing two million displaced people extremely exposed.
If the conflict with the rebels of the National Redemption Front escalates, the huge humanitarian effort to keep the displaced fed, clothed and provided for could collapse.
Less than a week ago, the UN's Emergency Relief Co-ordinator, Jan Egeland, warned that the work of the aid agencies could collapse because of a chronic lack of security.
That prediction has just come a step closer to realisation.
With the African peacekeepers now being asked to leave, a showdown between the rebels and the government seems to be on the cards.
Exactly how many troops the rebels can muster is unclear.
But they have had sufficient strength to continue holding out in the vast and desolate rural areas of Darfur, despite repeated government offensives.
One of the great weaknesses of the Darfur rebellion has been the splits between and within the various movements.
Minni Minawi's forces have been attacking their former rebel comrades
So when the peace deal was finally presented to the rebels in Nigeria in May, it was accepted by only one group: the faction of the Sudan Liberation Movement led by Minni Minawi.
His forces have now joined government troops in attacking his old comrades.
The rest of the rebel groups rejected the Abuja agreement, arguing that it did not offer enough power sharing or access to Sudan's oil wealth, for the people of Darfur.
These groups went on fighting, and in June they met in the Eritrean capital, Asmara, to form the National Redemption Front.
The declaration was signed by:
- Justice and Equality Movement leader Khalil Ibrahim;
- Dissident SLM faction leader Khamis Abdalla Abakar;
- Sudan Federal Democratic Alliance representatives Sharif Harir and Ahmed Ibrahim Diraige.
All said the May peace deal did not go far enough.
"We, leaders of political and military organisations abstaining from signing the Abuja document... reaffirm our rejection of that faulty process," read a group statement.
Former Darfur governor Ahmed Diraige became chairman of the new movement.
The Justice and Equality Movement says it "strongly condemns" the government decision to pull out the African Union force from Darfur.
Jem spokesperson Ahmed Hussain Adam said it "constitutes a clear breach" of previous agreements.