Those responsible for a deadly wave of explosions across Lebanon targeting paging devices used by members of the Hezbollah group “must be held to account,” the U.N. rights chief said Wednesday.

“Simultaneous targeting of thousands of individuals, whether civilians or members of armed groups, without knowledge of who was in possession of the targeted devices, their location, and their surroundings at the time of the attack, violates international human rights law and, where applicable, international humanitarian law,” Volker Turk said in a statement.