Unidentified armed men killed five police officers in an attack on security forces in northern Burkina Faso in the early hours of Sunday, in which around 15 of the attackers died, the security ministry said in a statement.

The incident occurred in Sourou province in the borderlands near Mali, where Islamist groups with links to al Qaeda and Islamic State have increased attacks in recent years despite international efforts to stamp them out.

The attackers struck at 5 a.m. and around 15 of them were killed in the ensuing fight, the ministry said.

Islamist attacks have surged across Africa’s Sahel region, killing thousands and driving millions from their homes in Burkina Faso, Mali and Niger. About 1.2 million people have been displaced by the violence in Burkina Faso alone.