Beirut. A week-old Turkish invasion of northeast Syria combined with a US withdrawal have redrawn the lines and left Russian-backed Syrian regime troops and Ankara's forces standing face-to-face.
What are the risks of an escalation?
Experts argue that an all-out conflict between Syrian regime forces and Turkey is unlikely but they do not rule out sporadic clashes.
Where the forces stationed?
On October 9, the Turkish army and its Syrian proxies launched a broad offensive against Kurdish forces controlling swathes of northeastern Syria.
The move against the People's Protection Units (YPG), a militia Ankara considers a terrorist group, came after US troops who were deployed along the border as a buffer between the two enemies pulled back.
Turkey and its proxies -- mostly Arab and Turkmen former rebels defeated by regime forces earlier in Syria's eight-year-old conflict -- have already conquered territory along 120 kilometres (75 miles) of the border.
In some areas, they have moved some 30 kilometres deep into Syria territory, prompting the Kurds to turn for help to the regime in Damascus.
Government troops responded and rushed north as soon as US troops withdrew from some of their positions, including the strategic city of Manbij.
The Syrian government's main backer Russia swiftly sent its own forces to patrol the new contact line between regime forces and the ex-rebels.
"It is mostly rebel groups linked to Ankara who are on the front lines, Turkish troops are mostly deployed along the border," the Syrian Observatory for Human Rights said.
The intense ballet of military deployments is redrawing the map of territorial control in a region previously held by the US-backed and Kurdish-led Syrian Defence Forces.
"There's a new map. And it's the regime sweeping almost everything, Turkey is left with a few crumbs along the border," said Thomas Pierret, from the French National Centre for Scientific Research.
- Risk of flare-up? -
Turkey insists it will not stop the offensive until it meets its declared goals of creating a buffer zone all along the border, but it now has limited room for manoeuvre in the face of the regime surge.
Russia and Iran, both Damascus allies, "will act as intermediaries to ensure everybody stays on the patch they have been allocated", said geographer and Syria expert Fabrice Balanche.
He said incidents should not be ruled out "due to the unclear nature of the territorial boundaries and the presence on the Turkish side of uncontrollable elements."
Two Syrian soldiers were killed near Ain Issa in artillery fire from Turkish proxies Tuesday, the Observatory said.
"There could be limited clashes... but no major battles," Pierret said. "The Syrian army cannot take on Turkey... The Turkish army is much better equipped."
"It isn't hard to imagine how areas retaken by the regime could be used as a staging ground for YPG guerrilla operations," he said.
The Kurdish force could be "reinvented as an anti-Turkey force" at Damascus and Moscow's orders. "It's a very credible scenario and could give Russia new leverage against Turkey."
- Informal deals? -
Moscow is keen to avert any escalation, analysts say.
"Russia is working overtime to prevent any type of large scale conflict between Assad's forces and Turkey and its proxies," said Nick Heras from the Center for New American Security.
Turkey together with Russia and Iran launched the so-called Astana process which provides a framework for peace talks on Syria.
To win support for its invasion, Turkey will need to make concessions over the Idlib region in Syria's northwest, Balanche predicted.
"The Russians finally agreed to this Turkish intervention in the north, in exchange for Idlib," he said, referring to the last opposition bastion in Syria, a region where Ankara has some clout but which Damascus wants to retake.
The strategic relationship between Ankara and Moscow goes far beyond the Syrian conflict. NATO member Turkey has ignored US warnings and acquired Russia's state-of-the-art S-400 missile defence system.
Turkish President Recep Tayyip Erdogan is expected in Moscow on Thursday for talks with his Russian counterpart Vladimir Putin.
Putin's office said a prior phone call between the two leaders had emphasised "the need to prevent confrontations between units of the Turkish army and Syrian armed forces".