Russia said it cannot guarantee the safety of Turkish aircraft over Syria, after Turkey shot down two Syrian war planes and struck a military airport, the latest clashes that have brought Moscow and Ankara closer than ever to direct confrontation.
Damascus said on Monday it was closing Syrian air space over the Idlib region, the last rebel-held sector of Syria, where fighting has escalated as Russian-backed government forces try to oust opposition fighters allied to Turkey.
The Kremlin said Turkey should take note of a warning issued by the Russian Defence Ministry overnight, which said Turkish aircraft could be at risk over the province.
Fighting in northwestern Syria has displaced a million civilians since December in what the United Nations says could be the worst humanitarian crisis of the nine-year war. Russian-backed Syrian government forces have launched a bid to capture the last swathe of Syria still held by rebels.
Moscow and Ankara both have forces in the area and have traded blame for the deteriorating situation since last week, when at least 33 Turkish troops were killed in an air strike, the worst attack on the Turkish military in nearly 30 years.
Russia, which has batteries of advanced S-400 surface-to-air missiles deployed in Syria, said the Russian and Turkish militaries were in constant contact over Idlib.
Syrian government forces are battling to recapture a strategic rebel-held town in Idlib. A Turkish official said Ankara would continue to strike President Bashar al-Assad's troops after escalating its military operations at the weekend.
Russia has long backed Assad, while Turkey supports anti-Assad rebels. The two countries both have forces in the area under a deal intended to avert all-out fighting there, but diplomatic efforts have crumbled in recent weeks.
Kremlin spokesman Dmitry Peskov confirmed on Monday that President Vladimir Putin and Tayyip Erdogan would hold talks on Syria in Moscow on Thursday. But Peskov said Russia had not changed its position on Syria and was as committed as ever to the Syrian government's fight against anti-Assad rebels.
Russia has been providing air support to Assad's forces in Idlib and also has special forces and military advisers on the ground in Syria. Private military contractors have also been fighting on Assad's side.
Russia "remains committed to the Sochi agreements (between Russia and Turkey on Syria), supports the territorial integrity of Syria, and supports Syria in its fight against terrorists," Peskov told reporters on Monday.