* Niger already has troops stationed near border
* Niger president urges troops to aid Malian civilians
* Fears of wider jihadist threat after Algeria plant raid (Adds details)
By Abdoulaye Massalatchi and Bate Felix
NIAMEY/BAMAKO, Jan 22 (Reuters) - An armoured column of Chadian troops in Niger moved towards the Malian border on Tuesday, part of an African military force that is gradually deploying to support French operations against Islamist rebels in northern Mali.
A Reuters reporter witnessed the Chadian forces, who are experienced in desert operations, advancing north from the capital Niamey on the road to Ouallam, some 100 km (60 miles) from the border, where a company of Niger's troops are already stationed.
France, which launched air strikes in Mali 11 days ago to halt a surprise Islamist offensive toward the capital Bamako, has urged a swift deployment of the U.N.-mandated African force to back up its 2,150-strong ground forces already there.
Niger President Mahamadou Issoufou, who visited the troops at Ouallam military base, condemned the al Qaeda-linked Islamist alliance controlling Mali's vast desert north. 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.
"I am confident in your burning desire for victory."
France says its troops will remain in Mali until they have completely dislodged the Islamist fighters from the north, amid concerns that the militants could use the vast desert area to launch terrorist attacks on the West and on neighbouring African countries.
Fears of this wider security threat from al Qaeda and its local allies in North and West Africa have increased sharply following a raid last week on a gas plant in Algeria by Islamist fighters. At least 37 foreign hostages were killed in the raid and its aftermath, when Algerian forces stormed the installation.
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.
Gao, the largest city of Mali's north, has been hit by French air strikes in recent days.
Niger has already sent a technical team to Mali, part of a battalion of 544 troops accompanied by six French liaison officers which it will deploy to Mali. (Additional reporting by Richard Valdmanis in Bamako and John Irish in Paris, Kader Maazou in Oualam; Writing by Daniel Flynn; Editing by Pascal Fletcher)