France says it has killed about 20 suspected fighters in a forest near Mali's border with Burkina Faso.

French Mirage fighter jets bombed several suspected arms depots in the Foulsare Forest, southwest of the northern Malian city of Gao, late on Saturday, a French counterterrorism unit said in a statement on Sunday.

Troops from Operation Barkhane, whose mission is to target fighters operating in the Sahel region of the Sahara Desert, said they also discovered large amounts of arms, ammunition, rocket launchers and explosives.

It however, did not identify the groups that were targeted.

A French soldier was killed last month in the region, considered a sanctuary of armed groups fighting the central government based in the capital, Bamako.

Set up in 2014, Operation Barkhane comprises around 4,000 soldiers who are deployed across five former French colonies - Mali, Chad, Niger, Mauritania and Burkina Faso.

In Niger, it operates four Mirage 2000 fighter jets and five Reaper drones for gathering intelligence.

France intervened in its former West African colony in January 2013 to stop a southward offensive by fighters linked to al-Qaeda who seized control of vast expanses of the north.

Despite continued French troop deployments, a UN peacekeeping mission and years of peace talks, Mali remains beset by unrest and ethnic strife.