MOSCOW (Bloomberg) - Russia's military campaign to save Syrian President Bashar al-Assad from being overthrown by rebels may have worked too well.
The Kremlin is discovering that it's losing influence over its protege as he grows increasingly confident about his survival.
In an effort to recover leverage, Russia is refusing to provide air support to enable Mr Assad to begin an assault on the last rebel bastion of Idlib, according to Russian lawmakers and Kremlin advisers.
The Russian stance, aimed at reinforcing its efforts to establish so-called de-escalation zones to strengthen a ceasefire in Syria, is creating a growing rift with Mr Assad, according to the officials.
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At the same time, they said the strategy to secure the zones may come unstuck amid spiraling political tensions with the US, which has so far backed Russian peace moves as part of an international focus on defeating Islamic State in Iraq and Syria (ISIS) in Syria.
Almost two years after President Vladimir Putin rescued Mr Assad from defeat and tipped the war in his favour by ordering an air campaign against rebel forces, he's faced with the dilemma of pressing the Syrian leader into accepting a symbolic power-sharing deal to end the six-year conflict and legitimise Russia's military presence.
As Mr Assad's grip on power has tightened, he's grown more reluctant to make any concessions to opposition groups at United Nations-led peace talks that resume in Geneva next month.
Russia's relations with Mr Assad are "tense now" because he's suspected of deliberately blocking the long-stalled negotiations in Geneva, said Mr Andrei Kortunov, head of the Russian International Affairs Council, a Moscow-based research group set up by the Kremlin.
"Russia isn't ready to allow Assad to wage war until victory," he said.
Mr Assad's forces are pushing toward the strategic eastern city of Deir Ezzor, which has been besieged by ISIS since 2015. The city offers control of the border with Iraq as well as oil and agriculturally-rich territory.
If the offensive is successful, it would free the Syrian army to turn its focus on Idlib in the north-west - though an assault would only be possible with the help of Russian air power.
"The Russians want to show they're in charge of their proxy," Mr Firas Abi-Ali, senior Middle East analyst at IHS Country Risk, said by phone. "But Assad's not going to yield without being bombed - he's not going to do it while he's winning territorially."
For the moment, the Syrian military is concentrating "on fighting Islamic State (in Iraq and Syria)", said Mr Rami Abdurrahman, head of the UK-based Syrian Observatory for Human Rights, an opposition monitoring group.
"Even if they wanted to take Idlib, they don't have the ability, because all the focus now is on Islamic State," he said, using an alternative name for ISIS.
Still, with the former Al-Qaeda wing gaining strength in Idlib while US-backed forces and Syrian government troops attack ISIS on different fronts, Mr Assad will be able to make the case that the city has to be captured to flush out terrorists, according to the IHS's Abi-Ali.
"The Russian strategy is not to let Assad take Idlib yet," he said. "Assad's strategy is to wait for Idlib until the jihadists take over completely."
Idlib is the last city with a major rebel presence since a Russian and Iranian-backed military campaign succeeded in wresting back full control of Aleppo, the former commercial capital, at the end of last year.
A major new offensive by Syrian government forces won't be successful without Russian bombing support from the air, said Ms Elena Suponina, a Middle East expert at the Russian Institute of Strategic Studies, which advises the Kremlin.
"The Syrian leadership has miscalculated whether Russia would provide them with assistance to take Idlib, as it did with Aleppo," she said by phone. "Moscow has decided to restrain the hotheads in Damascus because the priority now isn't the capture of Idlib."
US President Donald Trump on July 24 announced an end to the CIA programme providing what he called "massive, dangerous and wasteful" arms supplies to Syrian rebels fighting Mr Assad.
At their first meeting at the Group of 20 summit last month, Mr Trump and Mr Putin reached agreement on the US and Russia enforcing a ceasefire along with Jordan in southwestern Syria close to the Israeli border.
Mr Trump's policy of cooperating with Russia is hotly opposed by lawmakers from both Republican and Democratic parties, who passed legislation last week strengthening sanctions against Russia and giving Congress the power to block Mr Trump from lifting them.
The White House has indicated Mr Trump will sign the Bill, averting a likely override if he vetoed it. Russia in retaliation ordered the US to slash 755 staff, or almost two-thirds, from its diplomatic mission, risking a spiral of tit-for-tat counter-measures.
Mr Putin on Sunday (July 31) praised the Syrian ceasefire accord with the US, saying in an interview with state television that the two rival powers are "working and achieving results even now, even in this fairly difficult situation".
Three Western diplomats in Moscow, who spoke on condition of anonymity, said that Russia appears genuine about preventing an upsurge in fighting that would threaten efforts to establish the de-escalation zones. However, a senior US official expressed scepticism about Mr Putin's ability to restrain Mr Assad.
Holding onto some hope of influence, Russia is urging Mr Assad to refrain from "hasty steps," said Mr Frants Klintsevich, deputy head of the defense committee in Russia's Upper House of Parliament.