Meanwhile, NATO says it places a great emphasis on Turkey's security as the country is one of the most prominent members of the bloc.
The US does not support YPG militants in Syria's Afrin and does not see them as part of their fight against Daesh, Pentagon Spokesman Major Adrian Rankine-Galloway told Anadolu Agency on Tuesday.
"We don’t consider them as part of our Defeat ISIS [Daesh] operations which is what we are doing there and we do not support them,” Galloway said.
“Elements out of SDF areas are not receiving any train-advice assists from us. The groups that we support are exclusively are involved in operations countering Daesh", he added.
The Syrian Democratic Forces (SDF) which are dominated by the YPG militants. Turkey has long protested US support for the YPG, while Washington has brushed off its status as a PKK offshoot, calling it a "reliable ally" in its fight against Daesh in Syria.
Listed as a terrorist organisation by Turkey, the US and the EU, the PKK has waged a terror campaign against Turkey for more than 30 years.
Some 40,000 people have been killed in the clashes mainly concentrated in Turkey's southeast, as well as various attacks elsewhere in the country.
The Turkish military has also ramped up its presence and activities along the Turkey-Syria border following President Recep Tayyip Erdogan's call on YPG militants in the Afrin district of Syria's Aleppo province to surrender.
US Defense Chief Ash Carter had admitted in April 2016 that the PYD and YPG are linked to the PKK.
The head of the US special forces in 2015 had also urged the YPG to "rebrand" itself to avoid Turkish criticism and give the group a role in Syria's future. The PKK-linked group was then renamed the SDF, General Raymond Thomas said in July 2017.
Earlier last week, the Syrian Observatory For Human Rights (SOHR) stated that SDF released more than 400 Daesh members including commanders, who were brought from the countryside surrounding the eastern city of Deir Ezzor and the northeastern city of Hasakah.
"SOHR monitored that more than 120 members of them have joined the SDF," the monitor also said.
A former spokesperson for the YPG group, Talal Silo, who defected from the SDF and is now in Turkey had said the group was "just a name" that provided cover for the US to support the YPG.
Silo had also explained how the PKK-terrorist dominated force was formed and how the US made a controversial deal to allow Daesh militants to leave the city of Raqqa before it taken over by the US-backed forces.
US will not take part in Turkey's Afrin operation
The US-led coalition will not take part in the Afrin operation, spokesman for the coalition forces, Ryan Dillon told AA earlier on Tuesday.
"The coalition's mission has not changed: to defeat ISIS [Daesh] in designated areas of Iraq and Syria and set conditions for follow-on operations to increase regional stability," he said.
"We are not operating in Afrin. We are supporting our partners in defeating remaining ISIS [Daesh] pockets along the Middle Euphrates River Valley, specifically in areas north of Abu Kamal, on the eastern side of the Euphrates River," Dillon added.
His statement came in a response to Anadolu Agency's question as to whether the US or the coalition would support Afrin, where a Turkish operation is being seen as imminent, based on statements by Turkish leaders.
NATO says cares about Turkey's security
Meanwhile, NATO said it has a great emphasis on Turkey's security as the country is one of the most prominent members of the bloc.
“NATO strengthened Turkey’s air defense system against any possible missile threat from Syria. It developed airborne early warning and control system and boosted its military presence in the east of Aegean sea," a NATO official told AA.
"This proves that the NATO looks out for Turkey's national defense."
Earlier on Tuesday, Erdogan called on NATO to fulfill its responsibilities towards to its partners.
"NATO, you are obliged to take a stand against those who harass the borders of one of your partners," Erdogan said.
Turkey has been a member of NATO for over 65 years.