The US special envoy for Syria - James Jeffrey - has been in Ankara. He's been discussing how the United States and Turkey will create safe zones in Syria. The two countries share one broad aim, to make sure Daesh is fully removed and never returns. The problem for Ankara is that the Americans are using one terror group to fight another, because they back the YPG, the Syrian arm of the PKK. TRT World's Middle East correspondent Sara Firth reports.