The Turkish Foreign Ministry summoned the top US diplomat in the country, Philip Kosnett, to voice its disapproval over Washington's support for the People's Protection Units (YPG) in Syria on Wednesday.
A US State Department spokesman also confirmed the meeting took place, adding, "beyond that we aren’t going to read out any details of the conversation."
The summoning came following reports that US troops had begun to provide military training to some 400 YPG members.
Turkey is wary of the presence of Kurdish militants close to its borders in Syria, and has been opposed to US efforts to train and arm them in the Arab country. The US has promised to take back the weapons from Kurdish militants once the Takfiri terror group of Daesh, which the Kurds have been fighting, is routed in Syria.
The Kurds remain armed in the territory they have seized while fighting Daesh, nevertheless, even as Daesh is effectively defeated in the Arab country.
Ankara views the YPG as the Syrian branch of the militant Kurdistan Workers' Party (PKK) that has been fighting for an autonomous region inside Turkey since 1984.
The military support first began under US President Donald Trump’s predecessor Barack Obama, whose administration provided the so-called Syrian Democratic Forces (SDF) with weapons and training.
On Tuesday, Turkish President Recep Tayyip Erdogan said that his country is to continue its military operation in northern Syria to keep Kurdish militants away from Turkish borders.
The Turkish operation comes without the Syrian government’s permission, prompting repeated calls by Damascus to stop its military intervention.
Syria has been gripped by foreign-backed militancy since March 2011. The Syrian government says the Israeli regime and its Western and regional allies are aiding Takfiri terrorist groups wreaking havoc in the country.
Moscow has been providing air cover to Syrian army operations since 2014. Aided by the aerial support and Iranian military advisory assistance, government forces began reversing the terrorists’ gains.