A delegation led by the mayor of Banibangou was ambushed on Tuesday about 50 km (30 miles) from the town, near the border with Mali. The area is overrun by militants associated with a local affiliate of Islamic State that has killed hundreds of civilians in rural communities this year. A poverty-stricken, arid zone of west Africa encompassing the borderlands of Niger, Mali and Burkina Faso has been racked by violence in recent years as armed groups, some linked with al-Qaeda, have sought to establish control over communities and rid the region of local and international military forces. Thousands of...