French President Francois Hollande has said his country's forces are engaged in the "final phase" of the fight against militants in northern Mali.
He said there had been heavy fighting in the Ifoghas mountains, where members of al-Qaeda in the Islamic Maghreb (AQIM) were thought to be hiding.
Mr Hollande also praised Chadian troops for their efforts in the same area.
Thirteen Chadian soldiers and some 65 militants were killed in clashes on Friday, according to the Chadian army.
Chad's government has promised to deploy 2,000 troops as part of the African-led International Support Mission to Mali (Afisma).
Speaking in Paris on Saturday, President Hollande said "heavy fighting" was taking place in the far north of Mali, near the Algerian border.
"This is the final phase of the process since it is in that massif [the Ifoghas mountains] that AQIM forces have probably regrouped," he said.
"Our Chadian friends launched an attack yesterday which was very harsh with significant loss of life," Mr Hollande added. "I want to praise what the Chadians are doing."
The latest fighting was between Islamists militants and ethnic Tuareg in the In-Khalil area, near the border town of Tessalit.
The MNLA - a secular Tuareg group which seeks an independent homeland in the Sahara and Sahel regions of Mali, Libya, Algeria, Niger and Burkina Faso - was at one time allied to the Islamists but now supports the French-led offensive.
France has deployed 4,000 troops since 11 January to help the Malian government eject Islamist militants who seized control of the north of the country last year.
The French-led forces faced little resistance during the initial offensive, when they recaptured major towns of Gao, Kidal and Timbuktu.
Meanwhile, more help for the French and African forces is being offered by the United States, which is sending Predator drones to Niger.
The unarmed drones would be used to overfly the zone of combat in Mali and provide information about deployments, US officials said.