Beirut: Jihadists, who swept like an army across Iraq and Syria, are expected to return to guerrilla warfare and melt into the population to avoid heavy losses from US-led air strikes, analysts say.
The Islamic State group, which has captured large swathes of territory and committed atrocities such as beheadings and crucifixions, is expected to pull back to cities from sparsely inhabited areas where its fighters are easy targets.
IS militants are likely to "prepare defensive positions, particularly taking advantage of urban terrain for concealment", said Ben Barry, a military expert at the International Institute of Strategic Studies, a London-based think tank.
The militant organisation has taken control of important cities including Mosul, Saddam Hussein`s hometown Tikrit and Tal Afar in northern Iraq, as well as Fallujah and part of Ramadi in the west.
In Syria, they have a tight grip on Raqa, their stronghold in the north, as well as half of Deir Ezzor province in the east and a number of other areas.
But they are now expected to change their strategy as the United States leads a coalition of more than 50 nations -- mainly Western powers or Middle Eastern allies -- aimed at defeating IS.
French jets carried out their first air strikes against IS militants in Iraq on Friday, after US warplanes bombed a jihadist training camp.By blending into the cities, IS also hopes to increase the odds of civilian casualties to help its propaganda war, Barry believes.
"Their impressive media operations will seek to exploit (such deaths) to further alienate Sunnis from the (Shiite-led) Iraqi government and also to erode the international legitimacy of the international-led coalition," he said.
IS has already begun moving some fighters, particularly foreigners, from Iraq to Syria, according to Iraqi security analyst Ahmed al-Shreifi.
"They have kept only Iraqi fighters in Iraq because they can blend into the community more easily if military operations start against them."
In Mosul, jihadists have abandoned command centres established after they captured the city in June, moving to private homes in populous districts and keeping a low profile.
The same tactic is being used in Syria after US Defence Secretary Chuck Hagel told lawmakers that plans were being laid to hit targets there, including IS "safe havens".
In Deir Ezzor, jihadists have emptied the main regional arms depot and withdrawn from almost all their positions in Mayadeen further east, according to local activist Abu Osama.
Even oilfields have been left abandoned and the families of foreign fighters -- who once lived in residential buildings -- have been evacuated.
"They are following a tactic of disappearance," Abu Osama told a news agency via the Internet. "They leave spies behind, people who are from the local communities, who relay information to them."
In the northern province of Aleppo, IS fighters have withdrawn from their bases in Al-Bab, one of their main strongholds in the region.
IS cannot protect itself from US strikes so it must reverse its previous transformation from an underground "resistance movement to a quasi state", according to Richard Barrett, a former counter-terrorism chief at Britain`s foreign intelligence agency MI6.The only way that US aerial bombardment can make a significant difference now is on fronts where IS has concentrated its forces, such as in rebel-held Marea in the north of Aleppo, said Thomas Pierret, a Syria specialist at the University of Edinburgh.
He said that if the Americans strike, "IS will have no choice but to empty those areas and to allow advances by the rebels" who are battling both the jihadists and the regime of President Bashar al-Assad.
With 35,000 men in 215,000 square kilometres (86,000 square miles), IS militants will have to make choices.
"As the US strikes degrade the visible elements of the IS military structure -- command headquarters, trucks, artillery pieces -- I expect IS to morph back into an insurgency model where the IS fighters are intermixed with civilian populations," said Christopher Harmer, analyst at the Institute for the Study of War, a US think tank.
"That will make it more difficult for US air strikes to target IS fighters."
He said IS has shown itself capable of melting into the civilian population.
"I expect they will continue to use sleeper cells, snipers, car bombs, suicide vests, targeted assassinations. All of these tactics are virtually immune to air power," Harmer said.