The 29-minute video bears the official logo of Isis’s al-Furqan media arm, and purports to set out the militant group’s view of Christianity.

Starting with a description of the different branches of the church from Catholicism to Eastern Orthodox, footage includes the destruction of a number of churches, altars and works of art across a range of unspecified locations.

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.

Apart from the graphic killings, the video showed militants destroying churches and Christian iconography

An Isis militant smashes a cross on an altar Crosses and works of art were replaced with the black flag of Isis

Two groups of Ethiopian Christian captives are then shown. According to the subtitles, 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.

The video then switches between graphic footage of the captives in the south being shot dead and those in the east being beheaded on a beach.

Though the video could not immediately be verified independently, it has been promoted and trailed for some days now via Isis-affiliated Twitter accounts and resembled another from February which showed 21 Egyptian Christians being beheaded on a beach.

Rumours among Isis accounts that the new video would feature the London-born jihadist Mohamed Emwazi proved unfounded.

Ethiopia said it had not been able to verify that about 30 people shown in a video being shot and beheaded by the so-called "Islamic State" group were Ethiopian Christians.

"We have seen the video but our embassy in Cairo has not been able to confirm that the victims are Ethiopian nationals," government spokesman Redwan Hussein said. "Nonetheless, the Ethiopian government condemns the atrocious act."

He said Ethiopia, which does not have an embassy in Libya, would help repatriate its nationals if they wanted to leave the country.

Isis has only relatively recently gained a foothold in Libya amid the country’s chaotic civil war, where two governments backed by rival alliances of militias are battling each other as well as extremist groups.

Isis is also back on the march in Iraq, where it captured three villages near the city of Ramadi in the western Anbar province and remains locked in heavy clashes with Iraqi troops.