The leaders of Russia and Turkey will meet on Monday to discuss the fate of Syria's rebel-held Idlib, a critical issue on which the two key allies support opposing sides.
The meeting between Russia President Vladimir Putin and his Turkish counterpart Recep Tayyip Erdogan in the Russian resort city of Sochi will be the latest in a flurry of diplomatic meetings between world leaders aimed at preventing a humanitarian catastrophe ahead of an expected Syrian government assault on the last major rebel-held area of Syria.
The two leaders last met in Tehran on September 7 with Iranian leader Hassan Rouhani. Discord between them was caught on camera but while they failed to reach a ceasefire agreement on Idlib, there has been a recent lull in air strikes and a pro-Damascus source indicated a ground attack may not be imminent.
But Russia, Iran and the government of Syria still maintain that Turkish-backed rebels in Idlib are terrorists who must be eliminated.
Last week, Germany’s foreign minister met his Russian counterpart in Berlin on Friday where he pressed him to exert influence on Syria to avoid a catastrophe in Idlib.
Standing alongside Russian Foreign Minister Sergey Lavrov at a news conference, Heiko Maas said a military offensive could have "catastrophic consequences for millions of people."
Mr Maas said he and Mr Lavrov also discussed the possibility of President Bashar Assad's government using chemical weapons. He said: "it is clear to us that Russia has the ability to influence the Syrian regime, and we are counting on it now being used so that such use of chemical weapons is prevented under all circumstances."
In response, Mr Lavrov said Russia will use uncompromising force against what it calls terrorists. In a speech earlier Friday, he reiterated Russian suggestions that “terrorists” might stage chemical-arms attacks to try to implicate Assad and his backers.
In talks in Istanbul on Friday, officials from Turkey, Russia, France and Germany did manage to agree that any attack on Syria's rebel-held Idlib would have severe results and a political solution must be reached, according to Turkey's presidential spokesman.
Ibrahim Kalin also said that a refugee exodus from Syria would be a problem not only for Turkey but also for the European Union. Asked about Russian comments about opening humanitarian corridors from Idlib, Mr Kalin said it was too soon for such talk.
Meanwhile at least 20 fighters from a US-backed force fighting ISIS were killed Friday in an ambush in eastern Syria, a war monitor says.
The Kurdish-led Syrian Democratic Forces is waging an offensive around the town of Hajin in the province of Deir Ezzor, ISIS's last stronghold in the country's east.
"The fighters were advancing during a sandstorm, they were surrounded, ISIS members used explosives and opened fire," said the Syrian Observatory for Human Rights.
The US-backed SDF had been closing in on the ISIS pocket for months before formally launching its offensive on Monday.
Since then, 53 militants and 37 SDF fighters have been killed in fierce clashes, according to the Britain-based Observatory.
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ISIS once held nearly all of Deir Ezzor, but separate offensives last year by the SDF and Russian-backed regime forces left the militants clinging to a small area of territory near the Iraqi border.
The SDF estimates ISIS has some 3,000 fighters in its besieged holdout, many of them foreigners.
A senior US diplomat visited Kurdish-held territory in Syria last month and pledged Washington's lasting support.
"We are prepared to stay here, as the president [Donald Trump] has made clear, to ensure the enduring defeat of ISIS," Ambassador William Roebuck said.
ISIS once held swathes of territory across Syria and Iraq but has since seen its self-declared caliphate collapse.
The militants now control less than three per cent of Syria and are mostly present in the vast Badiya desert, which lies between Damascus and the Iraqi border.
On Monday ISIS fighters killed 12 Syrian regime fighters in an ambush in the southern province of Sweida. Eight militants were also killed, the Observatory said.