Speaking at a press conference, Nauert said those forces that the U.S. was working with “have familial relations, familial ties there, perhaps that's part of the reason why.”

Reiterating a previous statement, Nauert said, “What is going on in Afrin is taking away from the fight against ISIL,” and said the U.S. was in Syria “to fight ISIL”.

The U.S. has called the PYD/PKK a “reliable ally” in its fight against ISIL, despite strong protests by Turkey, which has highlighted the PYD/PKK’s continuing terrorist threat to both Syrians and Turkey’s border regions.

On Jan. 20, Turkey launched Operation Olive Branch to clear PYD/PKK and ISIL terrorists from Afrin, northwestern Syria.

According to the Turkish General Staff, the operation aims to establish security and stability along Turkey’s borders and the region as well as to protect Syrians from terrorist oppression and cruelty.

The operation is being carried out under the framework of Turkey's rights based on international law, UN Security Council resolutions, its self-defense rights under the UN charter, and respect for Syria's territorial integrity, it said.