Putin has long been a staunch defender of Assad, despite continuing and credible claims that the Syrian president has used chemical weapons against his own people.
The west is no friend of Assad but, awkwardly, it is aligned with him in fighting Islamic State. But despite the common enemy, U.S. Secretary of State John Kerry earlier this week warned his Russia counterpart, Sergei Lavrov, that Moscow's continued support for Assad "risks exacerbating and extending the conflict," a statement of the conversation said.
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Assad "could never be a credible member (of a coalition fighting ISIL),"Kerry said, adding that "there is no military solution to the overall conflict in Syria, which can only be resolved by a political transition away from Assad."
Some analysts believe Russia only wants to prop up the Assad regime, rather than help defeat IS.
Torbjorn Soltvedt, Principal Analyst, Middle East and North Africa at Verisk Maplecroft said in a note Tuesday that despite the rhetoric against Islamic State, "concrete measures taken by Russia have nonetheless focused on ensuring the survival of the Syrian regime."
"So far there is little to suggest that Russia is playing an important role in anti-Islamic State operations. The imminent delivery of a Russian-operated SA-22 anti-aircraft missile system to bolster the country's air defences, for instance, will be of no utility against the Islamic State," Soltvedt added.