Russia said on Saturday a Syria ceasefire plan was more likely to fail than succeed, as Syrian government forces backed by Russian air strikes took rebel ground near Aleppo and set their sights on the Islamic State stronghold of Raqqa province.
International divisions over Syria surfaced anew at a Munich conference where Russia rejected French charges that it was bombing civilians, just a day after world powers agreed on the "cessation of hostilities" due to begin in a week's time.
U.S. Secretary of State John Kerry reiterated accusations that Russia was hitting "legitimate opposition groups" and civilians with its bombing campaign in Syria and said Moscow must change its targets to respect the ceasefire deal.
The conflict, reshaped by Russia's intervention last September, has gone into an even higher gear since the United Nations sought to revive peace talks. These were suspended earlier this month in Geneva before they got off the ground.
Turkish forces shelled Kurdish YPG militia targets near the northern Syrian town of Azaz on Saturday, Turkey's Prime Minister Ahmet Davutoglu said, demanding that the group withdraw from land it recently captured.
The United States urged both Turkey and the Syrian Kurds to step back and focus instead on tackling the "common threat" of Islamic State militants who control large parts of Syria.
The Syrian army looked poised 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.
A Syrian military source said the army captured positions at the provincial border between Hama and Raqqa in the last two days and intends to advance further.
"It is an indication of the direction of coming operations towards Raqqa. In general, the Raqqa front is open ... starting in the direction of the Tabqa area," the source said.
Tabqa is the location of an air base captured by Islamic State two years ago, and the source said the army had moved to within 35 km (20 miles) of the base.
The cessation of hostilities deal agreed by major powers 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 war that has killed at least 250,000 people.
If its forces retake Aleppo and seal the Turkish border north of the city, 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 said 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.
ISLAMIC STATE TARGETED
Islamic State, driven by the goal of expanding its "caliphate" rather than reforming Syria - the original goal of the opposition when the conflict began as an unarmed street uprising in 2011 - is being targeted in separate campaigns by a U.S.-led alliance and Assad's government with Russian air support. Regional Kurdish forces supported by Washington are also fighting Islamic State in Raqqa province.
Gulf states that want Assad gone from power have said they would be willing to send in troops as part of any U.S.-led ground attack against Islamic State. U.S. Defense Secretary Ash Carter said on Friday he expected Saudi Arabia and the United Arab Emirates to send commandos to help recapture Raqqa.
Turkish Foreign Minister Mevlut Cavusoglu was reported as saying Saudi Arabia will send aircraft to Turkey's Incirlik air base to support the air campaign against Islamic State in Syria.
"Saudi Arabia is now sending planes to Turkey, to Incirlik. They came and carried out inspections at the base," Cavusoglu told the Yeni Safak newspaper, adding it was unclear how many planes would come and that the Saudis might also send soldiers.
Russian Prime Minister Dmitry Medvedev said on Saturday in Munich there was no need to scare anyone with a ground operation in Syria.
Two Syrian rebel commanders told Reuters on Friday insurgents had been sent "excellent quantities" of Grad rockets with a range of 20 km (12 miles) by foreign backers in recent days to help confront the Russian-backed offensive in Aleppo.
Foreign opponents of Assad including Saudi Arabia and Turkey have been supplying vetted rebel groups with weapons via a Turkey-based operations centre.
Some of these groups have received military training overseen by the U.S. Central Intelligence Agency. The vetted groups have been a regular target of the Russian air strikes.