the 29-minute video , titled ` until it came to them - clear evidence ' , shows dozens of militants holding two separate groups captive , thought to be in the south and the west of the country .
at least 16 men , described by islamic state as the ` followers of the cross from the enemy ethiopian church ' , are lined up and shot in a desert area while 12 others are filmed being forced to walk down a beach before being beheaded .
the victims inland are forced to kneel as militants dressed in combats and green masks stand behind them holding rifles .