Cavusoglu made the remarks to reporters after a meeting with opposition Republican People's Party (CHP) Leader Kemal Kilicdaroglu in the capital Ankara.
Asked about the Syrian Democratic Forces (SDF) and the terrorist PKK's Syrian affiliate PYD fighting Daesh to liberate the northern Iraqi city of Manbij, Cavusoglu said:
"The U.S., even President [Barack] Obama, assured Turkey that the PYD would return to east of the Euphrates River after Manbij's liberation. We expect them to keep their word," Cavusoglu said.
The SDF and PYD began operations to retake Manbij at the end of May. Approaching the city from the west bank of the Euphrates, the SDF and PYD besieged the city for two months.
The liberation of Manbij is important as it will cut off Daesh militants' key lines of communication between the Turkish border and Raqqa, Daesh’s self-declared capital.
However, Ankara does not recognize the PYD as a legitimate Syrian opposition movement. Turkey expects the group to vacate the west bank of the river after having seized control of the city from Daesh.
In June, Cavusoglu said that Turkey would not tolerate the forces of the YPG – the military wing of the PYD terrorist group – staying west of the Euphrates River. He said the U.S. promised that would not happen.
Turkish-Syrian border security and the advance of YPG-PYD forces in northern Syria have been key issues for Ankara. The two groups are designated terrorist organizations by Turkey but not the U.S.
Cavusoglu also said the U.S. Vice President Joe Biden will pay a two-day official visit to Turkey on Aug. 24. "Biden will visit instead of Secretary of State John Kerry," Cavusoglu confirmed.
Biden will be the most senior U.S. official to visit Turkey since last month’s defeated putsch. Joint Chiefs of Staff Chairman Marine Corps Gen. Joseph Dunford visited the country on Aug. 1.