NIAMEY/BAMAKO (Reuters) - Chadian forces advanced towards the Mali border on Tuesday as an African troop deployment and a U.S. military airlift swelled international support for French operations against Islamist rebels occupying the north of Mali.
The aim of the intervention is to prevent northern Mali from becoming a launchpad for international attacks by al Qaeda and its local allies in North and West Africa. Fears of this increased sharply after a hostage-taking raid by Islamist militants last week on a gas plant in Algeria.
Military experts say the swift and effective deployment of African forces is crucial to sustain the momentum of a French air campaign against the Islamists and prevent them melting away into empty desert or rugged mountains near the Algerian border.
An armored column of Chadian troops, experienced in desert operations, rumbled north from the Niger capital Niamey on the road to Ouallam, some 100 km (60 miles) from Mali's frontier, where Nigerien units are already poised to cross.
France, which launched air strikes in Mali 11 days ago to stymie a surprise Islamist offensive toward the capital Bamako, has urged a swift deployment of the planned U.N.-mandated African force to back up its 2,150 soldiers already there.
The number of French troops could be boosted to more than 3,000 in the coming days and weeks, a source with knowledge of the matter said on Tuesday.
An entry into Mali from Niger by part of the African force would widen the front of operations against the Islamist alliance in the north that groups al Qaeda's North African wing AQIM and the Malian militant groups Ansar Dine and MUJWA.
On Monday, French and Malian armored columns moved into the towns of Diabaly and Douentza in central Mali after the rebels who had seized them fled into the bush to avoid air strikes.
Niger President Mahamadou Issoufou, who visited the troops at Ouallam, condemned the Islamist alliance, and an imam, or Muslim cleric, said prayers for the troops.
"We are going to war. A war imposed on us by traffickers of all kinds, an unjust war, from which the peaceful citizens of northern Mali are suffering terribly," Issoufou told the forces.
France says its troops will remain in Mali until they have completely dislodged the Islamist fighters from the north and fair elections can be held in its former colony.
In support of the French, the United States has started transporting French soldiers and equipment to Mali from the Istres air base in southern France. Washington on Tuesday completed the fifth of an estimated 30 flights in an airlift expected to run for about a week.
A Reuters correspondent in Bamako saw a U.S. military cargo plane offload French soldiers, jeeps, and other equipment.
"We stand by our French allies," Pentagon spokesman George Little said in Washington. "We have carried more than 124 tonnes of equipment and supplies and more than 80 passengers."
Another Pentagon spokesman said the U.S. flights were helping to carry a French mechanized infantry unit to Mali.
Little said the United States had been providing France with intelligence since the outset of the operation, and was reviewing a request for aerial refueling tankers.
Britain, Belgium, Canada and Denmark were already transporting French materiel to Mali.
But, in a reflection of widespread fears of Islamist militant reprisal attacks, U.N. chief Ban Ki-moon warned the U.N. Security Council against requiring U.N. logistical support for combat operations in Mali. He said this would put U.N. civilian staff in the region at "grave risk".
France has also sent jet fighters and attack helicopters that have blasted rebel bases for more than a week, as it awaits troops from nearby African nations to deploy to the front line.
Some 1,000 troops from the West African regional bloc ECOWAS and Chad, a central African nation, have already arrived in Mali and that number is expected to top 5,000 in coming weeks.
Niger's armed forces, which completed their training a month ago, are expected to advance toward the rebel-held north Malian city of Gao in collaboration with the Chadian troops. It was not clear when exactly they would cross the border.
Niger has already sent a technical team to Mali, part of a battalion of 544 troops accompanied by French liaison officers.
Nigeria, Africa's top oil producer, also plans to deploy some 1,200 troops in Mali and its president, Goodluck Jonathan, said they would stay there until the crisis was resolved.
In an interview with Reuters in Geneva, Jonathan said Nigeria had a direct interest in intervening in Mali, pointing out links between the Nigerian Islamist sect Boko Haram and al Qaeda's north African wing in Mali.
"We believe that if we stabilize northern Mali, not just Nigeria but other countries that are facing threats will be stabilized," he said.
Colonel Oumar Kande, ECOWAS military and security adviser in Mali, told Reuters in Bamako the original plan for the U.N.-backed ECOWAS military intervention in the north was being changed to adapt to fast-evolving circumstances.
Instead of the Malian army alone playing the combat role, with ECOWAS supporting, now "everyone will fight", Kande said.
He added ECOWAS was concerned about its troops having to fight a difficult counter-insurgency war in a northern Mali desert and mountain battleground the size of Texas against Islamist fighters likely to shun a head-on conventional fight.
"Given the force of the reaction from the international community, they (the rebels) are likely to adjust and begin an asymmetrical war, ambushes, strikes by small cells," he said.
The insurgents have imposed sharia (Islamic law) in areas they control, carrying out amputations and at least one fatal stoning, and wrecking ancient shrines sacred to moderate Sufi Muslims.
International donors will be asked to finance training and support for the Malian, ECOWAS and other African troops involved in the deployment of the U.N.-backed African force AFISMA against the Islamist alliance.
Donors are to meet at a conference in the Ethiopian capital Addis Ababa on January 29 and France said they would be asked to provide about 340 million euros ($452 million).
Since the French started their operations earlier in January to block the jihadist thrust out of northern Mali, several thousand civilians have fled the recent fighting to neighboring states, the U.N. refugee agency UNHCR said. In Mauritania, 4,208 Malian refugees had arrived since January 11, it said.
Niger had seen 1,300 new refugees, while during the same period, Burkina Faso had received 1,829 refugees.
This was on top of almost 400,000 Malians displaced since April, when an offensive by Tuareg rebels allied with Islamist fighters seized Mali's largely desolate north following a military coup in Bamako in March.
Additional reporting by Bate Felix in Bamako and John Irish in Paris, David Alexander in Washington, Kader Maazou in Ouallam, Marina Depetris in Istres, Tom Miles and Emma Farge in Geneva; Writing by Pascal Fletcher and Daniel Flynn