French, Malian and UN forces have launched a "large-scale" operation in Mali, France's military says.
Spokesman Col Gilles Jaron told the AFP news agency that several hundred French soldiers were involved in the mission in the north of the country.
It was aimed at preventing a resurgence of "terrorist movements", he added.
On Wednesday, a suicide bomb attack on a UN Stabilisation Mission in Mali (Minusma) base in Tessalit killed civilians and two Chadian peacekeepers.
The UN Security Council stressed that those responsible would be held accountable and reiterated its support for Minusma.
The Malian leader of a splinter group of al-Qaeda in the Islamic Maghreb, Sultan Ould Bady, said it had attacked the base because the Chadians were "working for France".
France sent troops to oust Islamist rebels from northern Mali in January.
The rebels were quickly pushed back from the main urban centres. Some retreated to hideouts in the mountains and desert, from where they launch occasional attacks.
Col Jaron of the French military's general staff said the operation - called "Hydra" - was "the first time we have seen forces of significant size working together" in Mali.
Its goal was to "put pressure on any terrorist movement to avoid their resurgence", he added.
The colonel stressed that the mission was not linked to any recent attack.
"This is one those operations that are conducted regularly... to participate in the stabilisation of the country," he explained.
He did not say when the operation started or on which areas it was focused, nor provide exact numbers or details on the forces taking part.
A spokesman for the Malian army, Lt-Col Souleymane Maiga told the Reuters news agency: "It's an operation to sweep identified areas in the three northern regions [Timbuktu, Gao and Kidal]. It will last as long as is needed."
BBC Africa analyst Mamadou Moussa Ba says this is the first time French troops have publicly been involved in operations against Islamist militants in Mali for several months.
France has 3,200 soldiers in the country but plans to reduce the force to 1,000 by February, several months later than originally planned.
It handed over responsibility for security to Minusma in July. However, the UN force has less than half of its mandated strength of more than 12,000 military personnel and has appealed for reinforcements.