Some of the Bosniak population however sided with the Ustaše. Muslims composed approximately 12 percent of the civil service and armed forces of the Independent State of Croatia. Some of them also participated in Ustaše atrocities, while Bosniaks in Nazi "Waffen-SS" units were responsible for massacres of Serbs in northwest and eastern Bosnia, most notably in Vlasenica. At this time several massacres against Bosniaks were carried out by Serb and Montenegrin Chetniks.