Jihadi fighters have begun preparing defences against US air strikes and a feared land-based counter-offensive in Iraq and Syria, according to residents living under their rule.
Isil fighters are mounting barricades, increasing checkpoints and booby-trapping the roads into Mosul in northern Iraq, they said.
They have also begun sending their families out of the towns to safeguard them from the growing danger.
Air strikes by American and French fighter jets killed scores of men in an Isil training camp and an arms depot near the city on Thursday and Friday. Residents estimated the number of dead at anywhere between 60 and 200.
Isil has also evacuated command-and-control centres in both Mosul and Raqqa, the city in Syria which is the informal capital of Isil's "caliphate", and begun using Yazidi women captives as "human shields" in other key places.
"Two days ago, they left their main headquarters, and they moved to live inside our civilian neighbourhoods," said one Mosul resident, who asked not to be named.
"They took over all the houses abandoned by their inhabitants, such as the houses of the Christians, former officials and people who left the city. They also use the poorer houses as stores for weapons."
In Iraq, Kurdish Peshmerga forces in the north and Iraqi army and Iranian-backed militia forces nearer Baghdad have stabilised front lines and even pushed Isil back.
In Raqqa, their position is more secure and Isil has set up its headquarters in the ornate former governor's palace.
They have pushed Syrian regime forces out of a number of major bases, killing hundreds of captives, and have been besieging Kurdish towns to the north.
In Raqqa itself, residents said both they and the fighters were afraid of promised American air strikes. Isil was dispersing its military vehicles and men so they do not to become easy targets. "People are afraid of the air strikes, that they might be used as human shields or be bombed," said Abu Mohammed, a local activist who is still living in the Syrian city even though Isil has put a price on his head.
"Many people fled to the countryside or to Turkey. In my lane there are just 15 families left."
The Isil fighters are taking similar precautions of their own, he added. "When small planes for reconnaissance appear the jihadis hide. They even lock the doors of their headquarters.
"They also moved their families, their women and children, outside Raqqa."
In Mosul, where the local alliances that brought Isil to power are complicated, additional precautions are being taken by the jihadis against the risk of assassination of their leaders. There have been repeated reports of local anti-Isil hit squads attacking fighters.
The Mosul resident said four Isil fighters were killed in the middle of last week.
Some of the assassins turned Isil's puritan demands against them, disguising themselves under cloaks and niqabs, the full-face veil now demanded of women. (© Daily Telegraph, London)