The U.K.-based counter-extremism think tank Quilliam recently translated an ISIS propaganda paper outlining potential strategies the group could adopt in Libya. One possible approach involves taking advantage of Libya’s vast coastline and its proximity to Europe and travelling on the same routes as migrant boats to slip into Europe undetected.

“If this was even partially exploited and developed strategically, pandemonium could be wrought in the southern Europe,” Quilliam’s translation of the ISIS document reads. “It is even possible that there could be a closure of shipping lines because of the targeting of Crusader ships and tankers.” The researcher who translated the paper, Charlie Winter, notes the claims should be treated as propaganda, with no evidence that ISIS is actually employing this strategy.

Another concern is that fighters could join the refugee exodus fleeing across the Syria-Turkey border and make their way overland through Greece and the Balkans and into Western Europe.