So-called Islamic State's Libya branch has carried out another kidnapping, targeting a large group of Eritrean Christians who were traveling to Libya in hope of boarding a migrant boat to Europe.

The news was confirmed by a US defence official. Local media reports claim the migrants were kidnapped by militants south of the city of Tripoli, last Wednesday.

Three Eritrean migrants reportedly managed to escape from the kidnappers after the militants asked who in the group were Muslims and tested their knowledge of the Koran.

There were 12 Eritrean Muslims and some Egyptians in the group of 88 migrants.

Muslims in the group were in a separate truck from the Christians. 12 Eritrean Christian women were also separated from the main group.

The news comes after ISIS released a film in February showing the beheading of 21 captured Egyptian Christians on a similar beach, which immediately drew Egyptian airstrikes on the group's suspected positions in Libya.

ISIS then released a video in April, showing 30 Christians from Ethiopia being beheaded and shot on a beach and a forestry area in Libya.

This follows another video in February of the beheading of a group of 21 Coptic Christians on the beach in Libya, though that terrain was rockier than the one shown in the latest film.

It raises fears that ISIS is consolidating its presence on the 'doorstep of Europe', as Libya is just a few hundred miles from the coast of Italy

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ISIS kidnap 88 Eritrean Christians from smugglers

The video bore the official logo of the IS media arm Al-Furqan and resembled previous footage released by the extremist group.

Redwan Hussein, an Ethiopian government spokesman, said officials were in contact with its embassy in Cairo to verify the video's authenticity.

He said he believed those killed were likely to have been Ethiopian migrants hoping to reach Europe.

Libya has become a hub for migrants across Africa hoping to cross the Mediterranean to enter Europe for work and better lives.