By Mark Doyle
BBC World Affairs Correspondent
A UN force would have a stronger mandate than the AU peacekeepers
International mediators are pressing warring factions in the western Sudanese Darfur region to implement the peace agreement signed by some of them in the Nigerian capital, Abuja, last week.
The commander of the African peace monitoring military mission in Darfur, Nigerian Gen Collins Ihekire, said after the signing that it would take a month to put structures in place to implement the accord.
These would include monitoring a ceasefire and building a new
transitional regional government in Darfur.
Gen Ihekire also called, in an interview with Radio Nigeria, for an increase in the size of his force from 7,000 to 21,000 troops.
But there are massive hurdles to a lasting peace - both inside Darfur and in other parts of Sudan.
Some analysts say that unless there is a comprehensive agreement involving all warring groups across the country, including in Darfur, the agreement signed in Nigeria can't work.
There are insurgencies against the Khartoum government in every corner of Sudan, not just in the western region of Darfur; there are armed rebels in the east and in the north, and an only recently signed peace agreement in the south.
In Nigeria, the government of Sudan and one faction of the rebel Sudan Liberation Army (SLA), led by Minni Minnawi, signed an agreement which British International Development Secretary Hilary Benn - one of the mediators in Abuja - described as "an historic agreement" which everyone should welcome.
But another faction of the SLA, led by Abd-al-Wahid Muhammed Nur, refused to sign. Mr Nur told a London-based newspaper website, Al-Sharq al-Awsat, that the agreement "did not fulfil even our minimum demands".
Another rebel group in Darfur, the Justice and Equality Movement, also refused to sign.
Mr Benn said the agreement met a central demand of the Darfur rebellion by creating a regional transitional government which could be consolidated by a referendum on regional governance in three years time.
The British secretary of state said the two factions which did not sign were making "a profound mistake".
But Mr Nur said the agreement did not go far enough.
He said the people of Darfur deserved the right to nominate a vice-president in the central government in Khartoum and that the over two million people displaced by the government's scorched earth policy had a right to financial compensation.
Mr Nur also drew a parallel with the peace deal signed last year in Sudan's main north-south war which raged, on an off, for 50 years.
Some two million people have fled the fighting
Under that agreement last year the ethnic African Sudan People's Liberation Army (SPLA), which is separate from Darfur's SLA, agreed to peace in exchange for ministerial posts in the Khartoum government and the right to hold a referendum on southern independence in five years time.
Mr Nur said the war in Darfur had destroyed the infrastructure there, including all schools. He called for them to be rebuilt and for local languages and culture to be taught "as with the southern Sudan agreement".
This reference hints at the heart of Sudan's problem.
The long-running Darfur insurgency exploded into a rebellion in 2003 partly because the Darfurian groups thought the agreement to end the main north-south war, between the government and the SPLA, was ignoring their own perceived marginalisation in Darfur.
It was the crushing of the Darfur rebellion by the Khartoum-controlled central army, with help from Arab militia called Janjaweed, which caused the massive displacement of Darfurians within Sudan and across the border into Chad.
Now, some analysts say, it is possible that the partial Darfur agreement will, in turn, prompt yet another rebellion, by ethnic Beja rebels operating on the other side of the country in eastern Sudan.
This conflict, which has been largely ignored by the outside world, has the potential to create another crisis.
Rebel faction leader Mr Nur wants more concessions for Darfur
The Beja, too, feel marginalised from power in Khartoum and could see the partial agreement in Darfur as a template for them to follow - a template which would include a rebellion before signing a deal.
In the middle of all this is the Khartoum government, the core of which is the Islamist National Islamic Front (NIF) regime which came to power in a military coup in 1989.
Through its control of the army, and financed by oil revenues, this government has held the centre against a whole range of rebels which, together, see themselves as the "marginalised majority".
This majority has never coalesced into a working alliance, which has allowed the elite in Khartoum, drawn from a relatively small area around the capital, to stay in power.
Beja people are also angry about the underdevelopment of their region
One long-term possibility is that Khartoum will face a constant series of rebellions in various parts of the country, crisis-managing each by the use of military power or offering partial concessions.
Another possibility is that the international community will persuade the government to accept a United Nations force which could provide a more peaceful template for Darfur and other regions.
There is pressure from the United States for a UN peacekeeping force to take over in Darfur from the African military observer mission. But the government of Sudan has yet to agree to it.
The UN mission would in theory have a limited mandate.
But the Sudanese government suspects, probably correctly, that any expanded international presence would be hostile to the continued dominance in Khartoum of a relatively small, Islamist group which came to power in a military coup.