"We continue to engage the leadership on all sides in order to deescalate the situation," Robertson said on Monday. "The idea is to keep fight focus on ISIS [Daesh]."
The Syrian Democratic Forces have long been the point of disagreements between Turkey and the United States. Ankara has condemned Washington for sending arms and providing other support to the group while Washington has been calling on Ankara for restraint in its conflict with the Kurds.
The YPG makes up a major component of the Syrian Democratic Forces, which seek to defeat the Daesh terrorist group in Syria. The United States has been supplying the Kurds with weapons and sees its aid to the militia as part of the fight against terrorism.
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Turkey has said it considers the YPG to be a terrorist organization associated with the Kurdistan Workers Party (PKK), banned by Turkey. Ankara has been claiming that the YPG's presence near its border hampers its national security. Earlier this year, Turkey conducted an offensive against the Kurdish militia in Syria's northern border city of Afrin and is also engaged in an operation to eliminate Kurdish strongholds in northern Iraq.