Turkey has started joint patrols with Russia in northern Syria to verify whether Kurdish forces have withdrawn from a key border zone in compliance with a deal reached between the two governments.
The patrols, which began just before noon, follow an agreement they signed in the Black Sea resort of Sochi last week which gave Kurdish forces 150 hours to withdraw from a band of territory along the border, in a process that Russia said was now complete.
They add to the complicated mix of forces operating along the frontier, including US troops who patrolled an eastern section yesterday for the first time since US President Donald Trump said last month the troops were withdrawing.
Today, the patrols began near the border town of Derbasiyeh, from which Kurdish fighters have already pulled out.
The soldiers headed to the east of Derbasiyeh in a convoy of Turkish and Russian military vehicles to patrol a strip of territory several dozen kilometres long, according to Turkish military sources.
The Russian army said in a statement that the convoy consisted of nine vehicles, protected by an armoured personnel carrier, and that it would cover more than 110 kilometres.
The Turkish defence ministry confirmed in a tweet that the patrols "with ground and air units are underway".
The ministry said in a separate tweet that a meeting with a Russian military delegation was planned in Ankara to discuss "tactical and technical issues".
Last week's Sochi agreement halted a Turkish operation launched against Kurdish forces in northeastern Syria on 9 October, which left hundreds dead and prompted tens of thousands to flee their homes.
Under the deal, Turkey is to assume control over one 120-kilometre wide section in the centre of the border, while Syrian government forces are to deploy to the east and west.
Along the whole length of the border, a 10-kilometre-deep buffer zone is to be created on the Syrian side which will be jointly patrolled by Russian and Turkish troops.
Turkey intends to set up a "safe zone" 30 kilometres deep, in which some of the 3.6 million Syrian refugees it is hosting could be resettled.
The Kurds spearheaded a US-backed military campaign against the Islamic State group that deprived the jihadists' of their final sliver of Syrian territory in March this year but Ankara views the Kurdish forces as "terrorists".
Abandoned by their ally Washington - which early this month pulled its own troops back from the border area, effectively allowing Turkey to attack - the Kurds turned to Damascus which swiftly deployed its forces, reclaiming swathes of territory it lost as long ago as 2012.
Yesterday, President Bashar al-Assad said the Sochi agreement was "temporary," and will eventually pave the way for his government to retake Syria's northeast.
He said troop deployments were a prelude to reinstating central government control over the region in a process he said would be "gradual" and would "respect new realities on the ground".
Nearly 100 kilometres from the site of the joint patrols in Derbasiyeh, a convoy of five US armoured vehicles was seen patrolling on Thursday in a zone north of the town of Qahtaniyah.
The Britain-based Syrian Observatory for Human Rights said it was part of an eastern stretch of the border where US forces are seeking to maintain a presence.
"They want to prevent Russia and the regime from reaching parts of the border that lie east of the city of Qamishli," the de facto capital of Syria's Kurdish minority, Observatory head Rami Abdul Rahman said.
A spokesman for the US-led coalition said its forces are transiting on routes near the border as Washington "withdraws troops from northern Syria and repositions some troops to the Deir Ezzor region," near the border with Iraq.
Washington has begun reinforcing positions in Deir Ezzor province with extra military assets in coordination with the SDF to prevent the Islamic State group and others from gaining access to oil fields in the area, a US defence official has said.
Some 200 US troops are already stationed in Deir Ezzor.
President Trump this month has said a "small number" of US troops would stay to "secure the oil".