President Tayyip Erdogan said Thursday up to 250,000 migrants were fleeing toward Turkey from Syria's northwest Idlib region after weeks of renewed bombardment by Russian and Syrian government forces.

Turkey already hosts some 3.7 million Syrian refugees, the largest refugee population in the world, and Erdogan said it was taking steps with some difficulty to prevent another wave from crossing its border.

With winter worsening an escalating crisis, the United Nations has said some 284,000 people had fled their homes as of Monday. Up to 3 million people live in Idlib, the last rebel-held swath of territory after Syria's nearly nine year civil war.