At least 25 Malian soldiers are dead and 60 more are missing after militants attacked two army outposts.
Camps in the towns of Boulkessy and Mondoro near the border with Burkina Faso came under attack on Monday.
The government says their troops killed 15 militants and have since recaptured the area, but lost a lot of equipment.
Malian forces have now launched a joint operation with Burkina Faso and French forces in the region.
The West African country – along with Burkina Faso, Chad, Niger and Mauritania – is part of an anti-insurgency force supported by France known as the G5 Sahel.
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