Wikipedia:

The Tongo Tongo ambush occurred on 4 October 2017, when armed militants from the Islamic State in the Greater Sahara (ISGS) attacked Nigerien and American soldiers in Tongo Tongo, Niger, while they were returning to base from a mission. During the ambush, five Nigeriens, four Americans, and 21 militants were killed while eight Nigeriens and two Americans were wounded. The Nigerien and American soldiers were participating in a mission to gather information on the whereabouts of Adnan Abu Walid al-Sahrawi, the leader of the ISGS.