KIGALI, Rwanda

Twenty Nigerien soldiers and a civilian were killed in an attack by “a coalition of terrorist groups” in western Niger on Tuesday, the government said.

The incident occurred around 10 a.m. local time when a detachment of the Defense and Security Forces was attacked on the outskirts of the village of Tassia in the Tillaberi region in the tri-border area, the Defense Ministry said in a statement.

At least nine other soldiers were wounded, it added.

The military government declared three days of national mourning from Wednesday, during which flags will fly at half-mast.

The ministry said the army later launched an operation in which dozens of terrorists were neutralized and their means of transport destroyed.

Lt. Gen. Salifou Mody, the Minister of State for National Defense, in his condolence message assured the population of “the unwavering will of the defense and security forces to continue the fight for sovereignty.”

The Tillaberi region, which borders Burkina Faso and Mali, faces regular attacks blamed on an affiliate of the Daesh/ISIS terror group.

Niger is ruled by a junta which ousted democratically elected President Mohamed Bazoum last July, citing a worsening security situation.

Earlier this year, the junta cancelled “with immediate effect” a 2012 defense cooperation agreement with the US.