Ankara consider them as a "terrorist group" that threatens its security. Kosnett is the most senior US Embassy official in Turkey since Ambassador John Bass departed in 2017. His replacement has yet to be named.
Ankara believes YPG fighters are linked with Kurdistan Workers' Party (PKK) separatists inside Turkey, responsible for waging armed campaign since 1984 causing death to more than 40,000 people.
According to Aljazeera network, the People's Protection Units (YPG), the armed wing of Syrian Kurdish Democratic Union Party (PYD), is seen by Washington as the most effective ground partner for the US-led coalition fighting ISIL in Syria.
Wednesday's move was not the first time Turkey has expressed displeasure with the United States about the issue. This is also the reason for Vladimir Putin's telephone conversation with Recep Tayyip Erdogan.
Earlier on Wednesday, Turkish Foreign Minister Mevlut Cavusoglu had warned Russian Federation and Iran to adhere to their joint accord signed with Turkey a year ago for announcing "de-escalation zone" in Syrian town Idlib.More news: Diego Costa Scores On His Return To Atletico Madrid
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The latest push by the army and its allies has alarmed Turkey which has been deploying forces inside northern Idlib and setting up bases which it says are part of agreements with Iran and Russian Federation over a de-escalation zone in Idlib.
Turkey on Tuesday called the Russian and Iranian ambassadors to its ministry of foreign affairs to ask the envoys to urge the Syrian government in Damascus to end the border violations in the Idlib de-escalation zone.
Rebels launched a counter attack against Syrian government forces and their allies in Idlib province on Thursday, seeking to roll back an advance that is fueling tension with neighboring Turkey.
"If you are guarantors [of de-escalation] which you are, stop the regime", said the Turkish foreign minister in an interview with Anadolu news agency aired by the Turkish TV channels. Turkey, which guaranteed Idlib as a so-called "de-escalation zone, or a safe haven for the Syrian opposition, has protested the offensive on Abu al-Duhur and the mass bombardments".
Russia, Iran and Turkey are supposed to be the guarantors of last year's accord but Moscow and Tehran appear bent on reneging on their role to de-escalate fighting in the area, home to almost 2 million Syrians, to serve their own agenda.