Turkey's foreign minister says the United States has promised Ankara that U.S.-backed Syrian Kurdish forces will only be involved in a siege of the Islamic State stronghold of Raqqa but would not enter the city itself.

Mevlut Cavusoglu said Tuesday he hopes the U.S. would keep that promise. However, he says Washington had also pledged earlier that Syrian Kurdish fighters would withdraw from the town of Manbij, which has not happened.

He says Turkey prefers that "local" Arab forces enter Raqqa, backed by U.S.-led coalition and possibly including Turkish ground troops.

The remarks reflect Ankara's concerns over the expanding ground Kurdish fighters have gained in Syria as they battle IS militants. Turkey considers the Syrian Kurdish militia be a terror organization, saying it's an extension of Turkey's outlawed Kurdish rebels.