 The response of the NDH authorities to resistance had been to burn down the villages where this had occurred , and there were mass shootings of Serbs , which escalated the level of violence even further . In late May and June , 173 Serbs had been rounded up , tortured and killed in Nevesinje , and in early June , another 140 Serbs had been killed at Ljubinje . In response , Serbs attacked Ustaše officials and facilities , and conducted raids themselves , killing Muslim villagers . 
