Islamist militants killed four soldiers and nine civilian army volunteers when they ambushed a counter-terrorist operation in northern Burkina Faso on Thursday, the army said in a statement.
The troops, who were attacked in the centre-north province of Bam, fired back in retaliation and killed at least 34 assailants, it added.
Burkina Faso has been battling Islamist militants active in northern regions, some with links to al Qaeda and Islamic State, since 2015.
The fighting has displaced more than 1.85 million people in the West African country alone and killed thousands across the Sahel, where militant activity that took root in Mali has spread over the past decade.
Army officers angry about the escalating attacks overthrew Burkina Faso's president in January and vowed to improve security, but levels of violence have remained high.
Authorities in June ordered civilians to evacuate two large areas in its northern and southeastern regions ahead of anticipated operations against Islamist militants.
The army this month said it had accidentally killed civilians during a counter-terrorist operation near the evacuated zones.
(Reporting by Thiam Ndiaga; Writing by Sofia Christensen; Editing by Hugh Lawson)
