French troops are set for their first major ground combat with Islamist rebels in Mali after heading out from the capital Bamako.
France sent 750 troops Mali on Friday with the aim of halting an advance by the rebels and is expected to increase the number to 2500.
A convoy of about 30 armoured vehicles set out on Tuesday for Diabaly, a town captured by the rebels on Monday and 350km to the north.
The first units of an African force are set to arrive on Wednesday to bolster the French, the BBC reports.
Islamists entered Diabaly on Monday, taking the town from Malian forces. French war planes have since attacked the rebel positions, bombing the town of Gao,an important base for Islamist fighters who have taken control of much of the north of the country.
French defence minister Jean-Yves Le Drian has admitted that Malian forces around Diabaly have been struggling to combat well-armed rebels and that the central town of Konna had not been recaptured by government forces as had earlier been reported.
The West African force is expected to number about 3300. It will be deployed under UN Security Council resolution 2085, which was passed in December last year. A BBC correspondent said most of them have no experience of the sandy or mountainous conditions.
Meanwhile, a spokesperson for the separatist Tuareg organisation, the MNLA, in northern Mali says his group is ready to join the fight against its former allies, the Islamist militants.
Speaking to the BBC, Moussa Ag Assarid said his group was actively against al Qaeda and terrorism, but did not go as far as saying the MNLA would fight alongside French forces.
Moussa Ag Assarid said al Qaeda had been operating in northern Mali for 12 years with the collusion of some officials in Bamako.