YPG is 'Syrian offshoot' of PKK: US envoy
He spoke at a panel at the Defense One Summit, which brings top military, foreign policy and intelligence leaders to Washington to discuss American security throughout the world.
Jeffrey said U.S. operations in Syria could not be done without the "active participation, coordination, and cooperation of Turkey."
The U.S. is not able to function in the northeastern region of Syria while fighting Daesh forces at the same time, and to do both a local partner is needed, according to Jeffrey.
"That local partner since 2014 has been the PYD, which is the Syrian offshoot of PKK, but we have not designated it as a terrorist organization which we did with the PKK,” said Jeffrey, referring to the political wing of the YPG.
He said that the U.S. is still in the northeast region of Syria to defeat the Islamic State of Iraq and the Levant (ISIL), remove Iranians out of the area and ensure the political process in the country.
Turkey agrees with all three points but the U.S. added "some conditions" and did not do a proper job of explaining them to Ankara, he said without mentioning what those conditions were.
Jeffrey said without Turkey’s help, the U.S. mission in Syria would be over.
"Again, the mission will be finished," he added.
"The mission of trying to bring peace to Syria, if you turn your back, even on the Turks, or on our allies in the northeast which is the SDF, which is an evolution of the PYD, which in its own sense, is an offshoot of the PKK," said Jeffrey.