Transcripts of telephone intercepts published in Italy claim to provide evidence that ISIS is threatening to send 500,000 migrants simultaneously out to sea in hundreds of boats in a ‘psychological weapon’ against Europe if there is military intervention against them in Libya.

Many would be at risk of drowning with rescue services unable to cope. But authorities fear that if numbers on this scale arrived, European cities could witness riots.

Separately, the militants hope to cement their control of Libya then cross the Mediterranean disguised as refugees, according to letters seen by Quilliam the anti-terror group, reported by the Telegraph.