 The first indication that the situation had changed significantly was on 23 June , when a group of 200 Ustaše clashed with a group of rebels they estimated to number between 600 and 1 @,@ 000 . After an extended firefight near the village of Stepen , 5 km ( 3 @.@ 1 mi ) north of Korita , during which they suffered several casualties , the Ustaše also burned down four villages . They then entered two Muslim @-@ majority villages in the area and arrested 13 Serbs who had not been involved in the earlier fighting . The arrested Serbs were transported north to Avtovac and shot . That night , all adult Serbs above the age of 16 in Gacko , 4 @.@ 5 km ( 2 @.@ 8 mi ) northwest of Avtovac , were arrested , and 26 were immediately shot . The rest were transported 50 km ( 31 mi ) west to a camp in Nevesinje . Over the period 23 – 25 June , 150 Serbs from the village of Ravno , 30 km ( 19 mi ) southwest of Ljubinje , were arrested and killed at the gendarmerie post , and the remainder of the population fled to the hills . 
