Residents and local media report that the victim is a 73-year-old who was taken in the city of Agadez.
Strained relations between Abuja and Niamey have disrupted joint military patrols and allowed the armed group to expand.
Indigenisation efforts led by leaders more concerned with self-preservation than national progress often spell disaster.
The Economic Community of West African States hopes to use this time to convince the three nations to stay in the bloc.