“We have seen as the situation in Afrin has taken hold that some of those SDF forces … have started to leave their work with coalition partners, the fight against IS, and head over to Afrin to handle those types of issues,” Nauert said on Thursday. “That takes the eye off the ball on IS. It's a concern of ours.”

According to Sputnik news agency Nauert underscored that the SDF has been a tremendous and valuable fighting force in the fight against the IS.

Syrian Democratic Forces (SDF) fighters stand in the town of Tabqa, after capturing it from Islamic State militants this week.

The SDF said in a statement on Tuesday that they had decided to send fighters to the Afrin region to help the Kurdish People's Protection Units (YPG) militia there fight the Turkish army.

On January 20, the Turkish Armed Forces launched an operation against Kurdish forces in Afrin, an area in northern Syria controlled by the US-backed YPG.

Damascus has strongly condemned Ankara's actions, with the Syrian Foreign Ministry calling them a violation of the country's sovereignty.

Reporter’s code: 50101