A "terrorist group" attacked a unit of the VDP auxiliary force at around midday Wednesday near Belga, about 170 kilometres (105 miles) from the capital Ouagadougou, local sources said.

A regional VDP official said 12 had died and five were wounded, while "the enemy also suffered many losses."

A member of the force gave a figure of 13 dead and said the VDP was carrying out a "sweep with army support" against the assailants.

The deaths add to two attacks in the past week in the northern border region of Oudalan that claimed at least 70 lives among the security forces.

The landlocked Sahel state is battling a brutal jihadist insurgency that swept in from neighbouring Mali and is now in its eighth year.

More than 10,000 civilians, police and troops have died, according to NGO estimates, and more than two million people have fled their homes.

Around 40 percent of the nation's territory lies outside the government's control.

Anger within the military at failures to turn the tide sparked two coups last year, leading to the ascent of a 34-year-old captain, Ibrahim Traore, who has vowed to reconquer lost territory.

The Volunteers for the Defence of the Fatherland (VDP) is a key part of his strategy.

Set up in December 2019, it comprises civilian volunteers who are given two weeks' military training and then work alongside the army, typically carrying out surveillance, information-gathering or escort duties.

The force has suffered heavy casualties from roadside bombs and ambushes, strengthening the concerns of critics who say it is under-equipped and poorly trained.

Despite the losses, 90,000 people signed up in a recruitment drive last November that had sought 50,000 new members.