One of Australia's leading Middle East experts has branded as "a polite fiction" the idea that the West will negotiate with Russia even a gradual exit of the Assad regime in war-torn Syria.

Bob Bowker, a former long-serving Australian diplomat in the Middle East, said Russia needed to protect its interests such as its warm water port on Syria's Mediterranean coast and would not make a priority of attacking the Islamic State terror group as President Vladimir Putin has claimed.

With Moscow sending troops and military hardware into the disintegrating nation, Washington and its allies had little choice but to accept the reality that the Kremlin had the power to keep dictator Bashar al-Assad in place as its ally.

"I think it's a polite fiction. The Russian interest is in preserving the Alawite regime [of Assad] and they are under no pressure to remove Assad as the head of that regime," Professor Bowker said. "What we're now seeing is acceptance of some realities on the ground."

Western nations including Australia have softened their language in recent days about Mr Assad's removal, which was previously a precondition for any political dialogue on how to resolve the Syrian crisis.

However any Western support for a political solution would still demand that Mr Assad remain in power only on an interim or limited basis while a longer-term national unity government can be established.

US President Barack Obama told the UN General Assembly this week that the West needed to be realistic but "realism also requires a managed transition away from Mr Assad and to a new leader and an inclusive government".

Professor Bowker, who was Australia's ambassador to Cairo – which included responsibility for Syria – and is now with the Australian National University, said that with Russian support, Mr Assad could hold onto the Mediterranean coastal region – the heartland of his Alawite sect – even if he had to abandon the capital Damascus.

This meant Russia could keep its key Mediterranean naval facility at Tartus.

Professor Bowker backed the White House's caution about becoming embroiled militarily in Syria. While stressing Mr Assad was a "reprehensible figure", he said Mr Obama had been "very wise" to avoid committing itself to a conflict that had no clear political objectives.

Professor Bowker said the Russians had the power to protect the Assad regime on the coast, prevent no-fly zones being established and stop the formation of so-called "safe havens" that could be used by rebel groups as bases and "the Western countries really have no choice but to accept that outcome".

Rodger Shanahan, a former Army officer now with the Lowy Institute, said the softening of language on both sides could be a "precursor" to talks to resolve the crisis.

But for the foreseeable future, Mr Assad would likely stay in power and there would be only "backdoor co-operation" between Russia and the Western-led coalition to avoid coming into direct conflict in their respective fights against jihadists.

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