The 29-minute video released online Sunday shows two groups of dark-skinned captives. It says one group is held by an ISIS affiliate in eastern Libya and the other by an affiliate in the south.
A masked fighter delivers a long statement before the video switches between footage of the captives in the south being shot dead and the captives in the east being beheaded on a beach.
It was not immediately clear who the captives were.
The video bore the official logo of the ISIS media arm al-Furqan and resembled previous videos released by the extremist group.