The YPG has received arms shipments and training from the U.S., in a move that angered Turkey which considers the Kurdish forces to be a "terrorist group" that threatens its security.
The Turkish Foreign Ministry summoned on Wednesday the United States charge d'affaires to voice its disappointment over Washington's arming and training of the Kurdish People's Protection Units (YPG) in Syria, sources from the ministry said.
The de-escalation zones were set up last September in an effort to scale back the conflict. The Turkish Foreign Minister Mevlut Cavusoglu also called out Russian Federation and Iran to stick to the joint accord they signed with Turkey previous year agreeing on a "de-escalation zone" in Idlib which were set up to scale back the conflict. In 2016, the YPG-dominated Syrian Democratic Forces (SDF) pushed the Islamic State out of Manbij-a town on the western bank of the Euphrates-with support from the US-led coalition.
While the USA views the Peoples' Protection Units (YPG) militia as the most effective fighting force on the ground against Islamic State (IS) extremists, Ankara calls it a "terrorist" organisation linked to outlawed Kurdish militants in Turkey.
Lavrov noted that Moscow and Tehran have reached an important stage in preparation for implementing the initiative launched by Russia, Iran and Turkey to organize the Sochi Congress.
On January 9, the Russian and Iranian ambassadors were reportedly called to the Turkish Foreign Ministry in Ankara to receive a protest note. Military equipment is being deployed in Turkey's south-central province of Kilis, which borders Syrian territories controlled by the YPG and the PYD. A Syrian military source denied this and dismissed rebel talk of a counter attack as propaganda. "They will pay the price for it, if need be", reported Anadolu. The Russian defense ministry implied such technologies ware given to the rebels by Western (US) intelligence services and has rejected denials from the Pentagon to the contrary.
Damascus has been scoring military successes against the rebel groups in the area thanks to Russian air support and active involvement of Iran-backed militias.
Turkey-US relations strained over the latter's support for the PKK/PYD terror group's presence and arming of the group in the region.