The United States and Turkey working on a People's Protection Units (YPG)-free zone near the Turkish-Syrian border, and coalition forces left in the country following U.S. withdrawal will not take part in the safe zone, U.S. envoy for Syria James Jeffrey said Monday.

Speaking at a briefing at the State Department, Jeffrey said the U.S. recognizes Turkey's concerns about the threat posed by the PKK terrorists from their headquarters in Mount Qandil and that they do not want to see a second Qandil in Syria.

"We're working with Turkey to have a safe zone of some length along the Turkish border where there would be no YPG forces because Turkey feels very nervous about the YPG and their ties to the PKK.

"We understand that President [Donald] Trump has made that clear to President [Recep Tayyip] Erdoğan," he said.

Jeffrey noted that they are working on options that will address such concerns while also ensuring that it will not pose a threat to coalition partners dominated by the YPG, recognized by Turkey as the Syrian offshoot of the PKK terrorist group.

The PKK is listed as a terrorist organization by Turkey, the U.S., and the European Union.

Formed in 1978, the PKK terrorist group has been fighting the Turkish government for an independent state. Its terror campaign has caused the deaths of more than 40,000 people.

The PKK resumed its decades-old campaign in July 2015 after a three-year cease-fire collapsed. Since then more than 1,200 people, including security personnel and civilians, have lost their lives in PKK attacks.

Turkey has repeatedly criticized the U.S. for delivering weapons and military equipment to PKK's Syrian affiliate the YPG and its decision to perform joint patrols with the terrorist group.

Ankara has long told Washington that the YPG is no different from the PKK and partnering with one terrorist group to fight another is unacceptable.

To date, the U.S. has sent a total of 4,700 heavy weapons and armored vehicles to the YPG.

The YPG was the focus of Turkey's cross-border counterterrorism operation Operation Olive Branch earlier this year, in Afrin, Syria, near Turkey's southern border.