The only difference of opinion between Ankara and Washington on the Syrian conflict is the United States’ relations with Kurdish militias, U.S. Syria envoy Ambassador James Jeffrey said in an exclusive interview with Turkish daily Hürriyet on Thursday.

Turkey objects to the Unites States’ support for the predominantly Kurdish People’s Protection Units (YPG) and its umbrella organisation, the predominantly Kurdish Syrian Democratic Forces (SDF), accusing Washington of ignoring Turkey’s security concerns.

Turkey sees the YPG as an extension of the outlawed Kurdistan Workers Party (PKK), an insurgent armed group that has been fighting inside Turkey for more than 30 years, while the YPG forms the backbone of U.S.-led coalitions fighting against the Islamic State (ISIS) in Syria.

“Our differences with Turkey on Syria are just about our relations with the YPG and the PYD,” Jeffrey told Hürriyet.

The two NATO allies have been negotiating the establishment of a safe zone in northern Syria along the Turkish border, since the U.S. President Donald Trump announced in December his decision to withdraw American troops in Syria. Trump later said that the half of some 2,000 troops in Syria would stay in the country.

Turkey’s initial plan was for a 460-km (285 mile) wide and 32-km (20 miles) deep safe zone that will include Syria’s settlements to the north of Raqqa and settlements to the north of al-Hasakah.

“Now, we are in discussions for setting up what we call a safe zone, a safe zone on Turkey’s border but not in the eastern part (of the border). Because Turkey has concerns over the YPG,” Jeffrey said.

Meanwhile, Ankara wants the YPG to be cleared from a part of the region close to the border and for another safe zone to be established there, the diplomat said.

Jeffrey told Al Monitor this week that both Turkey and the SDF had agreed to pull back Kurdish forces and to establish the safe zone in northeastern Syria.