The loss of the highway between Mosul and Raqqa would be not just a logistical defeat for Islamic State but a psychological one, analysts say.

“The integrity of the caliphate — it’s built on continuous military victory,” said Jessica Lewis McFate, research director at the Institute for the Study of War, a Washington-based think tank.

The “caliphate” could lose legitimacy in the eyes of its supporters if it is unable to defend the land it has taken, she said.

Without their vital supply line, Islamic State operatives would be vulnerable in Mosul, which is increasingly isolated as Kurdish forces close in. They would also have to use alternative supply routes to Raqqa that meander through the harsh desert or expose them to dangers such as airstrikes by the U.S.-led coalition or confrontations with Iraqi security forces, analysts say.