The YPG, a backbone of the SDF, has led the fight against the militants of the extremist Islamic State group and has been a proven top U.S. ally in Syria.
Turkey is reported to have offered to guard the Kabul's international airport as questions remain on how security will be assured along major transport routes and at the airport, which is the main gateway to Kabul.
The Defense Department condemned Turkey's test of the Russian-made air defense system, saying it was not consistent with Turkey's commitments with a U.S. and NATO ally.