Turkey on Wednesday threatened to strike Syrian Kurdish militia forces if they do not withdraw from Manbij, a former bastion of the Islamic State (IS) group that has been taken over by predominantly Kurdish forces.

"We have said before we will strike the YPG if they do not retreat" from Manbij, Foreign Minister Mevlut Cavusoglu told journalists, referring to the Kurdish People's Protection Units. 

The YPG, which Ankara considers a "terrorist" organisation, is backed by the United States as the most effective fighting force on the ground in the battle against IS.