The 29-minute online video, titled “Until There Came to Them Clear Evidence”, 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 Koran.
The chief executioner speaks in English and says “our battle is a battle between faith and blasphemy”.
A narrator says: “To the nation of the cross, we are back again on the sands, where the companions of the Prophet, peace be upon him, have stepped on before, telling you: Muslim blood that was shed under the hands of your religion is not cheap.
“In fact, their blood is the purest blood because there is a nation behind them (which) inherits revenge. And we swear to Allah: the one who disgraced you by our hands, you will not have safety, even in your dreams, until you embrace Islam.”
Those executed were described as “the worshippers of the cross belonging to the hostile Ethiopian church”.
It is however unclear who the captives were or when they were captured.
Ethiopian Communications Minister, Redwan Hussein, said its embassy in Egypt is working to verify the video.
“We strongly condemn such atrocities, whether they are Ethiopians are not,” Hussein said.
“There are elements of IS around Ethiopia who are already carrying out operations, even though under a different name. We will keep on fighting them.”
Watch the footage below: