Chad has doubled its troops arriving in Niger to help local forces mount a new front to battle Islamists in the northern Malian city of Gao, from 200 to 400, a Chadian military source said Tuesday.

Speaking to AFP on condition of anonymity, the source said: "Presently we estimate that there are about 400 troops in Niger. Two hundred fully equipped men heading for Niamey crossed the border from Chad into Niger."

The rest of the 2,000-strong contingent Chad has pledged will have arrived in Niger by the first week of February, the source added.

The first of Chad's troops -- known for their hardiness and aptitude at fighting in desert conditions -- arrived in Niger on January 17.

They have been stationed at a base near the airport in the capital, Niamey, awaiting the order to deploy to Mali in support of a French-led offensive.

"Chadian and Nigerien troops will enter Mali via the Malian village of Labezanga, on the border with Niger, before heading for Gao. They will meet up with French and Malian forces at Timbuktu," the military source said.

Gao and Timbuktu, two of the biggest towns in northern Mali, have been under control of Islamist rebels for months, though some rebels have fled since the start of France's offensive on January 11.

Chad's troops will work closely with Mali's army and with a West African-led, UN-backed force which is currently taking shape.

Niger president visits troops ahead of Mali action
Ouallam, Niger (AFP) Jan 22, 2013 - Niger's President Mahamadou Issoufou on Tuesday paid a morale-boosting visit to troops preparing for battle in the key Islamist stronghold region of Gao, one of northern Mali's toughest areas of desert terrain.

"Nigerien armed forces in general, and your contingent in particular, have the physical, intellectual and moral capacities needed to overcome the enemy," Issoufou said in a stirring speech to forces currently stationed at Ouallam, around 100 kilometres (60 miles) north of Niamey, near Niger's border with Mali.

"This is a war we are going to win," he told them.

Now they have completed a month's special training with French military experts to prepare them for their mission, Niger's 500 troops will join the first soldiers of a 2,000-strong contingent pledged by Chad, whose troops are experienced in dealing with hard desert conditions.

Together they will head overland from Niger to Gao, Mali's army chief General Ibrahima Dahirou Dembele said Tuesday.

Recapturing Gao is seen as a key step in reclaiming Mali from the rebels.

African soldiers are being hastily assembled to form the International Support Mission in Mali (AFISMA) to help French and Malian forces fight rebels who have seized more than half of Mali's territory.

Gao -- like other key areas in the north -- has been subjected to strict sharia law by the Islamists.