The U.S. is aware of a Syrian-Russian convoy that traveled to the northern city of Manbij, the Pentagon confirmed Friday.
Spokesman Eric Pahon said Washington was informed by Russia of the vehicles' transit, through an established channel the countries use to avoid accidental clashes.
The U.S. is "very closely tracking that Russian movement", he said, noting that the convoy, which predominantly carried aid, was accompanied by "heavy equipment" for force protection in the highly contested area.
"It's a rapidly evolving situation and we're keeping an eye on it," said Pahon. "We don't want to cause any further instability in an already complicated battle space."
The U.S.-backed Syrian Democratic Forces (SDF) took control of Manbij from Daesh in August with the support of coalition air cover, and on-the-ground trainers and advisers.
The SDF is led by the YPG, a group the U.S. has consistently relied on as its principal partner in the anti-Daesh fight in northern Syria.
Turkey has designated the YPG as the Syrian offshoot of the PKK, also labeled by Turkey as a terrorist group. The U.S. and EU have similarly labeled the PKK, but has refrained from following suit on the YPG, vexing Ankara.
Turkey has insisted YPG elements leave Manbij and withdraw east of the Euphrates River.
Russian Lt. Gen. Sergey Rudskoy said earlier Friday the Syrian army would reach Manbij, and the YPG will leave the northern Syrian city to the Bashar al-Assad regime.
Rudskoy also said the Syrian government would administer state affairs in Manbij and the surrounding areas starting Friday.
The Pentagon said it has not been notified of such an agreement.
