FLAGS flew at half-staff and Koranic verses played on state media yesterday as Niger 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,…