Escalating military action by Russia and Turkey in Idlib risks a direct confrontation between the two major foreign powers in Syria's war, days ahead of a summit of their leaders to hammer out a deal to halt the fighting.
Both countries say they hope to avoid a head-on clash, but after Turkey ramped up attacks on Russian-backed Syrian forces and Russian military police helped secure a town seized from Turkey-backed rebels, all sides acknowledge the risk.
Turkey says it has shot down three Syrian planes and destroyed eight helicopters and scores of tanks since last Thursday, when 34 Turkish soldiers were killed in an air strike, the deadliest attack on the Turkish army in nearly 30 years.
In response to the Turkish assault and advances by Turkey-backed rebels, Moscow said on Monday that Russian military police had helped drive back rebels from Saraqeb and entered the strategic town which has changed hands three times in a month.
"We need to accept that this incident raised tensions between the two countries," a Turkish security official said of last week's attack on Turkish troops.
"Turkey does not intend to clash with Russia in any way, and Russia does not want that either," he said. "But on the battlefield it's another story. It's so complicated that an accidental attack on one another is the biggest risk."
- Why is Turkey threatening a full-blown conflict with Syria and to shatter its alliance with Russia
- U.S. willing to give Turkey ammunition for fight in Syria's Idlib
- Turkey shoots down third Syrian warplane in Idlib
NATO member Turkey has the alliance's second largest army. Russia, a nuclear-armed power, has a major air base in Syria and deployed warships in the Mediterranean last week.
Turkey already hosts 3.6 million Syrian refugees and is trying to stem advances by Russian-backed Syrian government forces which have displaced 1 million people in Idlib, the last rebel bastion in Syria, driving them towards the Turkish border.
Russian support since 2015 has been instrumental in turning the tide of the war in favour of President Bashar al-Assad, who says he will recapture "every inch" of Syrian land.
"Russia is taking a very tough stance and showing it's ready for conflict," said former Russian lawmaker Sergey Markov. "An attack on Saraqeb will be an attack on Russia."
STRENGTHENING NEGOTIATING HANDS
The showdown in northwest Syria comes ahead of Thursday's meeting between Presidents Tayyip Erdogan and Vladimir Putin, suggesting both sides are seeking to consolidate their military position in part to bolster their negotiating hand.
A Syrian opposition figure described the battle for Saraqeb, at the junction of Syria's main north-south and east-west highways, as a "war of wills", while a rebel military commander said both countries were trying to impose a "fait accompli".
"The Syrian government is trying to take over new places with Russian support ahead of the Erdogan-Putin meeting," the Turkish security official said. "They are trying to have the upper hand at the table".
Turkey insisted last month that Syrian forces withdraw to Idlib frontlines established in a 2017 "de-escalation" accord. Damascus and Moscow ignored the demand, taking more territory in a conflict they frame as a war on terrorists.
Vladimir Frolov, a former senior Russian diplomat, said the key issue at Thursday's summit was the size of the remaining pocket of border territory which Russia would allow rebels to hold and where millions of displaced people could shelter.
"Erdogan wants a 30 mile deep zone, Moscow has been offering an 8 mile strip," Frolov told Reuters, predicting that the two leaders might split the difference.
He said Russia's deployment in Saraqeb was a signal that the control of the north-south M5 highway on which the town stands was a "red line" for Moscow, and would remain under its control.
That would require Turkey to back down from a months-long refusal to abandon a dozen military observation posts set up around the perimeter of the de-escalation zone, most of which are now surrounded by Syrian government forces.