A two-day mourning period has been declared after 41 people were killed in Burkina Faso earlier this week.
Civilian fighters from the Homeland Defence Volunteers was ambushed on Thursday in a remote area in the northern Loroum province.
The group is funded by the government and trains to contain insurgents.
Authorities have faced repeated protests in recent months over their perceived failure to curb a four-year insurgency, that has killed thousands across Africa’s Sahel Region and forced more than a million people to flee their homes.
Burkina Faso’s armed forces killed about 100 militants in a joint operation with Niger between November 25 and December 9 in the two countries’ border zone, the Burkinabe army said.
The operation involved hundreds of troops deployed on both sides of the border, an army statement said. They arrested about 20 suspects, seized guns and hundreds of motorcycles, and destroyed about 15 improvised explosive devices, it added.
Islamist militants linked to al Qaeda and Islamic State are waging an insurgency in Burkina Faso, Niger and neighbouring Mali which has killed thousands of civilians and displaced about two million in the last few years.
The insurgents have inflicted heavy casualties on the region’s armies, and killed 53 people at a gendarmerie post in Burkina Faso last month in the worst strike on security forces in years. Since then, more soldiers have been killed almost every week in scattered attacks.