"The Turks have reassured us many times that they have no intention -- no intention whatsoever, from President Erdogan personally on down today -- of staying in Syria very long," James Jeffrey, the US special representative on Syria, told reporters on board Secretary of State Mike Pompeo's plane.

He was speaking on his way to Israel from Ankara, where President Recep Tayyp Erdogan promised US Vice President Mike Pence that Turkey would suspend military operations for five days so fighters from the Kurdish YPG militia could pull out.

According to the two sides, Turkey would enjoy a 32-kilometre (20-mile) deep "safe zone" on its border free of the YPG, whom Erdogan links to Kurdish separatists at home.

While Pence said that the YPG's move out of the zone had already begun, Jeffrey acknowledged that the Kurdish fighters -- close allies with the US in the fight against the Islamic State movement -- were not happy.

"We're basically doing our best efforts to get the YPG to withdraw using as a carrot and a stick the sanctions levers that we have," Jeffrey said.

"There's no doubt that the YPG wishes that they could stay in these areas," he said.

But he said that Turkey promised that it was only seeking to remove YPG fighters, not the Kurdish population as a whole.

"We hope that there will be no mass movement of people," Jeffrey said. "We were very, very strong and very, very insistent on that."