ISTANBUL (Reuters) - Turkey-backed forces have besieged the Islamic State-held Syrian town of al-Bab from the west and have set their sites on Manbij for their next offensive, Turkish President Tayyip Erdogan said on Tuesday.

In a speech in the capital Ankara, Erdogan said YPG Kurdish militia forces must completely leave Manbij. Erdogan, who views the Syrian Kurdish fighters as hostile forces, also accused Kurdish militants of trying to turn Iraq's Sinjar into a base. He said Turkey will not allow Sinar to become a "terror centre".

(Reporting by Humeyra Pamuk; Writing by David Dolan; Editing by Daren Butler)