Unidentified shooters have killed at least 14 members of a government-backed civilian militia in an ambush in northern Burkina Faso, the latest attack in a surge of escalating violence.

The incident came as President Roch Marc Kabore faces increasing criticism over his handling of a years-long security crisis that has killed thousands of people, displaced more than a million and left an immense humanitarian crisis in its wake.

In a statement on Thursday, the government said the gunmen had attacked the militia about 10km (6.2 miles) from the town of Titao, where they were heading to reinforce other civilian fighters.

The 14 killed were members of Burkina Faso’s Homeland Defence Volunteers, which receives funds and training from the government to help contain armed groups linked to al-Qaeda and ISIL (ISIS) that have also been operating in neighbouring Niger and Mali.

There was no immediate claim of responsibility.

Opposition and civil society groups have repeatedly expressed their dissatisfaction with the government’s management of the security crisis, taking to the streets to call on Kabore to step down.

On Wednesday, Prime Minister Christophe Joseph Marie Dabire tendered his resignation to Kabore, a move that triggered the resignation of the entire government, as stipulated by law.

Kabore has been under pressure to make changes and has already reshuffled his army leadership, but critics say the dismissals critics are an attempt at deflecting responsibility.

Last month, 49 military police officers and four civilians were killed in an attack by an al-Qaeda affiliated group, marking one of the worst attacks on the military in recent memory.