The 29-minute online video purports to show militants holding two groups of captives. It says one group is held by an IS affiliate in eastern Libya known as Barka Province and the other by an affiliate in the south calling itself the Fazzan Province.

A masked fighter brandishing a pistol delivers a long statement, saying Christians must convert to Islam or pay a special tax prescribed by the Quran.

The video then 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 or when they were captured. It was also not clear how many captives were killed.