U.S. Vice President Joe Biden delivers a speech in Riga, Latvia, August 23, 2016. Thomson Reuters

ANKARA (Reuters) - The United States has made it clear to Syrian Kurdish forces that they must return to east of the Euphrates river after seizing control of the Syrian town of Manbij to retain U.S. support, Vice President Joe Biden said on Wednesday.

Biden was speaking during a visit to Turkey. Ankara has said it expects Syrian Kurdish fighters to withdraw across the river after the Manbij victory by the U.S.-backed Syria Democratic Forces (SDF), an alliance of Kurdish and Arab fighters. Ankara considers the Kurdish YPG in Syria as a hostile force.

Biden also said Turkish officials made clear that the rule of law will prevail during an investigation into the July 15 failed coup. Turkey has detained and arrested tens of thousands after the coup, worrying Western allies who fear a crackdown on dissent.

(Reporting Jeff Mason; Writing by Patrick Markey; Editing by David Dolan)