Analysts say huge uncertainties ahead

"There are clearly huge uncertainties, there’s a real risk that initial strikes move to something wider since IS is so embedded," said Julian Barnes-Dacey, fellow in the Middle East and North Africa Programme for ECFR.

"There’s no clear path toward pushing back against IS through an air campaign, you can contain them through air strikes, but with their breadth of territory and the way they are seen by some as the only legitimate opposition to Asad, air strikes can only take you so far," he told MEE.

"There’s no way IS can be defeated quickly, heavy air strikes first aimed at their visible positions, hardware, beyond that they will need a long-time campaign based on local alliances, that may mean some kind of alliance with Asad," added Barnes-Dacey.