French troops are set for their first major ground combat with Islamist rebels in Mali after heading out from the capital, Bamako.
A convoy of about 30 armoured vehicles set out on Tuesday for Diabaly, 350km (220 miles) to the north, a town captured by the rebels on Monday.
The first units of an African force are set to arrive on Wednesday to bolster the French.
France intervened last Friday to halt the Islamists’ drive to the capital.
‘Determined adversary’
Islamists entered Diabaly on Monday, taking the town from Malian forces.
French war planes have since attacked the rebel positions.
French Defence Minister Jean-Yves Le Drian confirmed on Wednesday that French troops had headed north.
The BBC’s Mark Doyle in Bamako says the convoy of armoured personnel carriers set out with guns at the ready; at some points along the road, people gathered to wave at the French soldiers.
Mr Le Drian has admitted that Malian forces around Diabaly have been struggling to combat well-armed rebels.
He also admitted that the central town of Konna had not been recaptured by government forces as had earlier been reported.
He said: “We are up against a determined adversary that is well-equipped and has not given up, but we have hit them hard with our strikes, including those deep in their territory.”
Our correspondent says the French or their allies in the Malian army need to take control of both Konna and Diabaly if their campaign is to advance.
France has some 800 troops on the ground in Mali and defence sources said their numbers were expected to increase to 2,500.
However, France has been pushing hard for the deployment of a West African regional force.
Regional military commanders began a meeting in Bamako on Tuesday, agreeing the swift deployment of troops.
A company of 190 Nigerians will be the first to arrive, on Wednesday.
Nigeria will lead the force, with 900 troops. Benin, Ghana, Niger, Senegal, Burkina Faso and Togo have also pledged to take part.
The West African force will total about 3,300 under a UN Security Council resolution.
Tuareg offer
In March and April last year, Islamist and secular Tuareg rebels overran the main population centres in northern Mali. Soon the Islamists, some with links to al-Qaeda, took control and imposed a hardline form of Sharia.
While a West African force was being planned with the aim of bringing the north back under the control of the Malian government, the rebels began moving further south.
It was the rebel capture of Konna last Thursday that prompted France’s military intervention.
French air strikes have since blocked the rebels, who have moved back to an area between Douentza and Gao.
Air raids have also reportedly sent the rebels fleeing from two of the main northern towns, Gao and Timbuktu.
On Wednesday, an official of the separatist Tuareg organisation, the MNLA, in northern Mali, said the group was ready to join the fight against their former allies, the Islamist militants.
Speaking to the BBC, Moussa Ag Assarid, did not go as far as saying the MNLA would fight alongside French forces but said his group was against al-Qaeda and terrorism.