US-backed Syrian fighters have turned over several villages in the country's north to government forces under a deal to avoid conflict with Turkey, a spokesman told AFP on Tuesday.
The Manbij Military Council, part of the US-backed Syrian Democratic Forces, announced the planned handover last week.
"Some villages and points on the western side of the town of Al-Areima have been handed over to the border guards of the Syrian regime," Manbij Military Council spokesman Sherfan Darwish told AFP.
He said the handover was carried out "with the goal of curbing Turkey's expansion and its occupation of Syrian territory, and to... prevent the shedding of civilian blood."
He declined to give further details but the Syrian Observatory for Human Rights, a Britain-based monitor of the war, said the handover had happened on Monday and involved fewer than 10 villages.
Observatory director Rami Abdel Rahman described the handover as "for show."
"Members of the Manbij Military Council simply put on army clothes and raised the Syrian flag to avoid friction with the Turks," he told AFP.
There was no mention in Syrian state media of the handover to government forces.
The Manbij Military Council, part of the Kurdish-Arab SDF, first announced the handover last week, marking the first time that US-supported fighters had proposed ceding territory to regime forces.
The Council said the deal had been agreed with Russia to "protect the line dividing the Manbij Military Council and the areas under the control of the Turkish army and Euphrates Shield."
Euphrates Shield is the name of the operation Turkey launched inside Syria last August targeting the Islamic State group and the SDF, which is dominated by Kurdish fighters that Ankara sees as "terrorists".
The handover plan was announced after Euphrates Shield forces attacked several villages under SDF control east of the town of Al-Bab last week.
Turkish President Recep Tayyip Erdogan said last week that the operation's next target would be Manbij -- a former IS bastion that is now under SDF control.
But on Monday, Ankara stepped back from that threat, saying it would not act without cooperation from Russia and the United States.
The profusion of forces operating in Syria has led to a deeply complex battlefield and tensions between different parties.
Washington said on Monday it had sent additional troops into Manbij to deter rival powers from targeting each other rather than IS.
"This is obviously a really complicated situation," said Pentagon spokesman Navy Captain Jeff Davis.
"We have made visible actions in deploying US forces as part of the coalition in and around Manbij to reassure and deter -- that's to deter parties from attacking any other parties other than ISIS itself," he said, using another acronym for IS.
More than 310,000 people have been killed in Syria since the war began with anti-government protests in March 2011.