MOSCOW: Vladimir Putin thinks Russian air strikes in Syria have helped turn the war's tide but the pace of the Syrian army's advance has frustrated him, some sources say. If Aleppo falls, he could get the military and symbolic prize he has been craving.

More than four months of Russian air strikes have stabilised the government of President Bashar al-Assad, the Kremlin's closest Middle East ally, helping his forces find momentum on the battlefield.

But the names and strategic significance of the towns and villages they have recaptured have failed to electrify a Russian public more worried about falling living standards. Nor has the Syrian army - backed by Russian air power - yet delivered a major victory that Russia can sell to the wider world as proof of its military might and growing Middle East clout.

"There has been some frustration with the Syrian army's performance," one source close to the Russian military, who declined to be identified, told Reuters. "Particularly in the beginning they were making slow progress."

Retaking full control of Aleppo, Syria's biggest city before the five-year war, would change the narrative, say diplomats and analysts, bringing Putin a step closer to his preferred end-game which envisages a Russia-friendly Syrian government that allows Moscow to keep its naval and air base there.

"So far we've heard reports of government forces gaining ground here and there and there have been a few notable successes," Dmitry Trenin, a former colonel in the Russian army and director of the Carnegie Moscow Center, told Reuters.

"But all those successes were rather tactical and not particularly spectacular," said Trenin. "Should Aleppo be placed under full control of Damascus that would be a big psychological boost for Assad and a source of satisfaction for the Kremlin."

Aleppo has been divided for years, with government forces controlling a section and other parts in the hands of rebels.

Tens of thousands of Syrians fled intensifying Russian bombardment around Aleppo on Friday, and aid workers said they feared the city, which once held two million people, could soon fall under complete government siege.

Government troops and their Lebanese and Iranian allies fully encircled the countryside north of Aleppo and cut off the main supply route linking the city to Turkey in the last 24 hours. Ankara said it suspected the aim was to starve the population into submission.

As the Kremlin's impatience for a breakthrough has grown, it has bolstered its forces in Syria. Mostly recently, local media reported it had dispatched its most advanced military jet -- the Sukhoi-35s -- to join its strike force of around 40 fast jets.

It has also intensified its strike rate.

'USEFUL DISTRACTION'

A victory in Aleppo could help lift morale at home where an economic crisis is eroding living standards and real incomes are falling for the first time in Putin's 15 years in power.

Boosted and protected by a loyal state media, a tightly-controlled political system and a dearth of meaningful opposition, Putin's approval rating remains over 80 percent according to opinion polls.

But with tentative signs of social discontent bubbling up -- foreign currency mortgages holders, truckers and pensioners have all protested in recent months -- a headline-grabbing Russia-assisted victory in Syria could cheer downcast voters.

"It would be a useful distraction and a show for people," said Stepan Goncharov, of independent pollster, the Levada Center, saying state media had in the past used Syria to stoke anti-Western feeling and to reinforce the idea that Russia is again a great power.

"Their trick is to remove themes that stir social anxiety and replace them with ones that unite," said Goncharov. "A military victory (in Aleppo) would be a great power moment, a symbol of military might, and would be used to increase support for the authorities."

He said the last time Levada asked, in October, they found that 72 percent of Russians had a broadly positive opinion of Russian air strikes in Syria, but that the subject had since taken a back seat to stories about the economy and what the Kremlin was doing to navigate the economic crisis.

There were some signs support for the authorities was slipping a little because of the downturn, he added.

Carnegie's Trenin said Russians, despite the Kremlin's flashy media campaign, were not actually that interested in the Syria conflict and with memories of the Soviet debacle in Afghanistan still lingering wanted the Kremlin to limit its involvement there.

"For most people this is a war in a distant country," said Trenin, saying voters remained nervous about any suggestion that ground forces might be sent. So far, the official Russian military body count has been just four, three of whom were killed in combat.

However, Islamic State claimed it blew up a Russian passenger plane over Egypt in October, killing all 224 people onboard, in revenge for Russia's Syria campaign.

For Putin, says Trenin, Syria is important but part of a wider play.

"The ultimate goal of Mr Putin is to restore Russia to great power status," he said. "Syria is part of that. But it's also about wider Russian foreign policy and about Putin's own legacy. Syria is the place where this is being decided."