The senior commander and spokesman for the US-backed Syrian Democratic Forces (SDF) has defected from the group, handing himself over to the Turkish-allied Free Syrian Army, Reuters reported on Wednesday.
Brigadier General Talal Silo, a Turk and the public representative of the Kurdish-led forces, arrived in the city of Jarablus in the north of Syria before being escorted to Turkey.
"Silo was secretly coordinating with commanders from the FSA and when he entered areas under their control he then crossed into Turkish territory," Ibrahim al-Idlibi, an FSA spokesman said.
The coalition released a statement, saying only that it was "aware of reports of Talal Silo's apparent departure from the SDF, but have no further details on his current status at this time."
The SDF is dominated by the Syrian Kurdish People's Protection Units (YPG), which Turkey views as a "terror" group linked to the outlawed Kurdistan Workers' Party (PKK). Silo had previously led the Seljuk Brigades, which was comprised of Syrian Turkmen.
Whilst no reason for the departure has been officially given, tensions have emerged between Arab and Kurdish groups in recent weeks as the fight against Daesh draws to a close.
Local Arab tribes in the region have accused the Kurdish militias of discrimination and conscripting their youth as soldiers; the YPG denies the allegations.
Turkey has long lambasted the US for working with and arming the YPG as the main US ally in the fight against Daesh.
Earlier this week, Ankara said it was appalled by the approach of the US Department of Defence towards an agreement between the Syrian Kurdish YPG militia and Daesh to withdraw Daesh militants from the Syrian city of Raqqa.
However, the US has indicated that it has no immediate plans to scale back its activities or exit the region, with Defence Secretary James Mattis stating on Monday that the US military will fight Daesh in Syria "as long as they want to fight".