Flags flew at half-staff as Niger Republic began observing three days of national mourning for the 137 victims of coordinated raids on villages in the southwest.

The killings on Sunday represented Niger’s worst civilian carnage in recent memory, surpassing an attack by suspected militants in January that killed at least 100 villagers and another last week that killed at least 58.

The scale of the violence this year has called into question claims of progress in the fight against Islamist militants by governments in West Africa’s Sahel region and former colonial power France, which has 5,000 troops there to support them.

A security source blamed Sunday’s attacks, which were carried out by men on motorbikes in the remote Tahoua region near the border with Mali, on the local Islamic State affiliate. Islamic State has claimed responsibility for previous raids against security forces and French aid workers.

Sisanda Mpiti.