The U.S. support for the YPG/PKK-dominated Syrian Democratic Forces (SDF) has been damaging its partnership with Turkey, Mark Kimmitt, the former assistant for the secretary of state for political-military affairs under George W. Bush’s term said Friday.

"I’ve never heard the United States issue a denial of the links between the YPG and the PKK," Kimmitt told a broadcast on CNN Türk TV channel, referring to the Syrian offshoot of the PKK terrorist group, which has been waging a war against the Turkish state for over four decades.

He continued by noting that the secretary of defense during the Obama administration had even admitted there were links between the two.

The U.S. has primarily partnered with the YPG in northeastern Syria in the fight against Daesh. Turkey strongly opposes the YPG/PKK’s presence in northern Syria, which has been a major sticking point in strained Turkey-U.S. relations. The U.S. has provided military training and thousands of truckloads of weaponry to the terrorist group, despite its NATO ally’s security concerns.

Kimmitt continued by saying that the partnership has "unfortunately" been damaging Washington’s relations with Ankara, and that he would hope that the two sides found a middle way, but they have not reached that point yet.

Touching upon Turkey-NATO relations, Kimmett said Turkey has one of the largest armies in NATO and it was important for the country to stay in the alliance. However, he expressed concern about Ankara’s purchase of Russian-made S-400 missile defense systems, as he referred to technical issues that may expose the technological data.

"We need to solve this problem. Defense Secretary Austin and Defense Minister Hulusi Akar have been trying to solve this issue," he said, adding that the two figures are capable of solving it.

Ties between NATO allies Turkey and the United States were badly strained in 2019 over Ankara’s acquisition of the advanced S-400 Russian air defense system, prompting Washington to remove Turkey from its F-35 Lightning II jet program.

The U.S. argued that the system could be used by Russia to covertly obtain classified details on the Lockheed Martin F-35 jets and is incompatible with NATO systems. Turkey, however, insists that the S-400 would not be integrated into NATO systems and would not pose a threat to the alliance. Defense Minister Akar also said that the S-400 will not be integrated into NATO systems.

The Russian-made S-300 system, for instance, has been sold to 20 countries, including NATO member countries such as Bulgaria, Greece and Slovakia.

The S-300 system, completed in 1978, is designed to defend against short- and medium-range air attacks and is considered one of the world’s most powerful air defense systems.

In 1996, Greece signed a deal with Russia for the purchase of S-300s for deployment on Greek Cypriot soil.

These missiles could not be deployed in southern Cyprus as a result of Turkish pressure, but in 1998, they were deployed in Crete, whose strategic importance has been rising steadily.

Greece also signed new agreements with Russia in 1999 and 2004 to purchase TOR-M1 and OSA-AKM (SA-8B) medium – and low–altitude air defense systems.

These Russian-made air defense systems are currently an integrated part of Greece's air defense system and have also been deployed by the Greek Cypriot administration.