Militants killed 41 people last week in an attack in northern Burkina Faso, including the prominent leader of a volunteer group helping the country's military, the government said.

Alkassoum Maiga, the government spokesman, announced two days of mourning following the deadly ambush on a convoy in Loroum province on Thursday.

Among the victims was Soumaila Ganame, also known as Ladji Yoro. Burkina Faso's President Roch Marc Christian Kabore said Ganame had died for his country and must be a model of our determined commitment to fight the enemy.

"The death of Burkina Faso's most important volunteer leader has created a sense of panic," said Heni Nsaibia, a senior researcher at the Armed Conflict Location & Event Data Project.

While Ganame achieved legendary status as a popular counter-insurgent who played a central role in mobilising (volunteers) in Loroum and Yatenga, he was also the embodiment of the absent state," he said.

Violence in the once-peaceful West African nation is escalating as attacks linked to al-Qaeda and the Islamic State increase.

More than 50 gendarmes were killed in November in the largest attack on the country's security forces in recent memory and at least 160 civilians were massacred in the Sahel region in June.

"Even though Burkina Faso's security forces are conducting the most operations compared to its neighbours in the volatile Sahel region, the army is overstretched, putting out one fire at a time," Nsaibia said.

Volunteer fighters have been accused of committing some human rights abuses against those suspected of fighting with the jihadis, but also have become the targets of attacks.

The government is facing calls to step down amid its inability to stop the violence, with weeks of protests taking place in November.

In response, the president fired his prime minister this month.