DERBASIYEH, Syria, — Turkey started joint patrols with Russia in northern Syria Friday to verify whether Kurdish forces have withdrawn from a key border zone in compliance with a deal reached between Ankara and Moscow.

It follows 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 Syria's border with Turkey, in a process that Russia said was now complete.

Amid this joint patrol came the news that at least 13 people have died Saturday in a car bomb blast near a market in the Syrian border town of Tal Abyad controlled by Turkish forces, Ankara and a rights watchdog said.

Turkey's Defense Ministry said 13 civilians were killed and another 20 people injured in the attack, which it blamed on Kurdish fighters.

The Britain-based Syrian Observatory for Human Rights meanwhile reported the deaths of 14 civilians and Turkish-backed rebels in the explosion.

The joint patrols add to the complicated mix of forces operating along the frontier, including US troops who inspected an eastern section on Thursday for the first time since US President Donald Trump said last month his country was withdrawing.

They began on Friday near the border town of Derbasiyeh — from which Kurdish fighters have already pulled out — and lasted around four hours, an AFP correspondent on the Turkish side of the border reported.

The soldiers had headed to the east of Derbasiyeh in a convoy of Turkish and Russian military vehicles to patrol a strip of territory several dozen kilometers long, according to Turkish military sources.

The Russian army said in a statement that the convoy consisted of nine vehicles, protected by an armored personnel carrier, covering more than 110 kilometers (68 miles).

Turkey intends to set up a "safe zone" 30 kilometers deep, in which some of the 3.6 million Syrian refugees it is hosting could be resettled.

United Nations Secretary General Antonio Guterres said he would "consider the proposal", stressing the need for the "voluntary, safe and dignified" return of refugees, during a visit to Istanbul on Friday where he met with President Recep Tayyip Erdogan.

Last week's Sochi agreement between Ankara and Moscow halted a Turkish operation launched against Kurdish forces in northeastern Syria on Oct. 9, which left hundreds dead and prompted tens of thousands to flee their homes.

Under the deal, Turkey is to assume control over one 120 kilometer (75 mile) wide section in the center of the border, while Syrian government forces are to deploy to the east and west.

Along the whole length of the border, a 10-kilometer deep buffer zone is to be created on the Syrian side which will be jointly patrolled by Russian and Turkish troops.

The Kurds spearheaded a US-backed military campaign against the Islamic State group that deprived the militants 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 last 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 swaths of territory it lost as long ago as 2012.

President Bashar Al-Assad said Thursday the Sochi agreement was "temporary," and will eventually pave the way for his government to retake Syria's northeast.

UN Syria envoy Geir Pedersen on Friday voiced hope over talks in Geneva between the Syrian government, opposition and civil society.

Pedersen said he was "very impressed" that the sides were meeting at all to discuss amending the country's constitution ahead of possible elections as part of a UN peace plan.

Nearly 100 kilometers (around 60 miles) 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.

Trump last month said a "small number" of US troops would stay to "secure the oil". — AFP