The AU is in the process of expanding the strength of the mission, known as AMIS, sevenfold, to some 3,320 personnel, including 450 military observers of a shaky ceasefire signed by Khartoum and two rebels groups in April.

It was expected that 237 Rwandan troops would set off Saturday, joining 155 already on the ground in Darfur.

"The rest will be airlifted in the coming days," Rwandan Defence Minister Marcel Gatsinzi said at Kigali airport.

On Thursday, 47 Nigerian troops flew in to Darfur as part of the expansion operation.

On October 20, the AU's Peace and Security Council resolved that the enhanced AMIS will have a renewable one-year mandate. The main role of the troops is to protect the military observers but they are also charged with protecting civilians under certain, not entirely clarified, circumstances.

Tens of thousands of people are estimated to have been killed in Darfur -- an area the size of France -- since two rebel groups rose up in February 2003, prompting a robust response from government forces and allied militia.

US Secretary of State Colin Powell used the word "genocide" of the scorched earth practices of the local Arab mounted militia who have been razing villages and attacking people of black African descent.

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