Syrian peace envoy Kofi Annan arrived in Moscow on Saturday to gauge how far Russia was willing to push its Arab ally after joining a UN call on regime forces to pull back from protest cities.

Annan will meet President Dmitry Medvedev and Foreign Minister Sergei Lavrov on Sunday and then hold talks starting Tuesday in China -- the other Security Council member resisting efforts to condemn Syrian President Bashar al-Assad.

The UN-Arab League envoy is carrying the embattled leader's answer to a peace plan under which Syria could begin a "political transition" to a representative government, with no specifically defined role for Assad.

Moscow backed Wednesday's non-binding Security Council statement in support of the initiative only after making sure it contained no implicit threat of further action should Assad fail to comply.

Washington's UN ambassador Susan Rice admitted that the UN call represented only "a modest step" towards ending a year of bloodshed in Syria that the opposition says has claimed more than 9,100 lives.

But it came amid growing signs that Moscow was beginning to lose patience with Assad in spite of his commitment to massive new Russian arms purchases and the granting of key naval access to the Mediterranean Sea.

A top Kremlin-linked lawmaker said Assad should treat the UN statement as "an insistent recommendation" whose implementation would determine the future course of relations between the two countries.

"Assad has to take the first step: he must pull the Syrian army out of large cities," the lower house of parliament's foreign affairs chief Mikhail Margelov said this week.

"Russia's future position on the conflict will depend on how successfully (the Syrian government) complies with the provisions spelled out in the Security Council statement," said Margelov.

But analysts have warned that Russia's interests in Syria are too important for it to allow Western and regional powers to independently dictate the battle-scarred nation's fate.

Russia not only sells billions of dollars in arms to Syria but also relies on Damascus to lobby its interests in a region where Moscow has lost much of its influence in recent years.

Medvedev's office said ahead of Annan's arrival that halting the bloodshed was impossible "without ending the foreign supply of arms to the opposition and its political support".

Yet Russian officials appear to be preparing for Assad's eventual departure even while refusing to accept his loss of full legitimacy -- a stance taken by most Western powers since last year.

"Assad's position is difficult," one unnamed Kremlin official told Interfax on Friday. "I do not know whether he has prospects or not. But no one is predicting another 10 years in power for him."

The dramatic shift in tone but persistent refusal to join international calls for Assad to go means that "Russia is not wedded to this regime," said Kommersant foreign affairs correspondent Maxim Yusin.

"Russia's main goal is to make sure that Assad's opponents do not grab all the power -- this would see Russia lose everything it has in Syria," said Yusin.

"Annan's visit should tell us what Russia is willing to do should Assad not listen on this occasion."

Russia's immediate plans include a meeting next week with members of a moderate opposition group called the National Coordination Committee for Democratic Change in Syria.

The alliance has previously refused to join the Syrian National Council's calls for urgent international intervention and appears to be viewed more favourably by the Kremlin.

"We think this organisation is no less -- and probably more -- influential than the Syrian National Council," said Deputy Foreign Minister Mikhail Bogdanov.