The Syrian army looked poised on Saturday to advance into the Islamic State-held province of Raqqa for the first time since 2014, apparently to pre-empt any move by Saudi Arabia to send ground forces into Syria to fight the jihadist insurgents.
The cessation of hostilities deal falls short of a formal ceasefire, since it was not signed by the warring parties - the government and rebels seeking to topple President Bashar al-Assad in a five-year-old war that has killed 250,000 people.
If its forces retake Aleppo and seal the Turkish border, Damascus would deal a crushing blow to the insurgents who were on the march until Russia intervened, shoring up Assad's rule and paving the way to the current reversal of rebel fortunes.
Russia has said it will keep bombing Islamic State and the al Qaeda-linked Nusra Front, which in many areas of western Syria fights government forces in close proximity to insurgents deemed moderates by Western states.
Russian Foreign Minister Sergei Lavrov, asked at a security conference in Munich on Saturday to assess the chances of the cessation of hostilities deal succeeding, replied: "49 percent."
Asked the same question, his German counterpart Frank-Walter Steinmeier put the odds at 51 percent.
The complex, multi-sided civil war in Syria, raging since 2011, has drawn in most regional and global powers, caused the world's worst humanitarian emergency and attracted recruits to Islamist militancy from around the world.
Assad, backed on the ground by Iranian combatants and Lebanon's Hezbollah in addition to big power ally Russia, is showing no appetite for a negotiated ceasefire. He declared this week that the government's goal was to recapture all of Syria,though he said this could take time.
The U.S. government said Assad was "deluded" if he thought there was a military solution to the conflict.
Syrian state television announced the army and allied militia had on Saturday captured the village of al-Tamura overlooking rebel terrain northwest of Aleppo.
The Syrian Observatory for Human Rights reported advances in the same area, adding that Russian jets had hit three rebel-held towns near the Turkish border.
Government offensives around Aleppo have sent tens of thousands of people fleeing towards the Turkish border.