Islamist militants killed 15 Burkinabe soldiers and volunteer militiamen on Saturday as they returned from a supply mission in eastern Burkina Faso, the army said on Sunday.
A further four soldiers were wounded in the attack in Gourma province, while 11 are still missing, it said in a statement.
Burkina Faso has been battling militants, some with links to al Qaeda and Islamic State, since 2015.
The worsening violence spurred soldiers last month to overthrow the government in the country’s second coup this year.
The crisis has displaced almost 2 million people in Burkina Faso alone and killed thousands across West Africa’s Sahel region, where an insurgency that took root in Mali has spread over the past decade.