Turkey on Monday blasted an agreement between YPG/PKK militants in Syria's northeast and a US oil company as "unacceptable" and equivalent to terrorism financing.
Senior Washington officials have confirmed that a US oil company has signed an agreement with the YPG-led Syrian Democratic Forces (SDF) to "modernise" oil fields under its control.
Syria already condemned the deal as "theft" and an "affront to (its) national sovereignty" on Sunday.
The SDF is a YPG-led paramilitary alliance that backs a semi-autonomous administration in northeastern Syria and controls the country's biggest oilfields.
The US-backed SDF is mostly made up of the YPG which Turkey considers to be a "terror group" linked to the bloody-minded PKK.
"We deeply regret the US support to this step, disregarding international law, violating territorial integrity, unity and sovereignty of Syria, as well as being considered within the scope of financing terrorism. This act, which cannot be justified by any legitimate motive, is utterly unacceptable" the Foreign Ministry said in a written statement.
Turkey's remarks came after media reports that the US-based company Delta Crescent Energy LLC signed a contract with the SDF for oil extraction, processing, and trade in the northeastern parts of Syria.
"By this step, the PKK/YPG terrorist organization has clearly demonstrated its ambition to advance its separatist agenda by seizing the natural resources of the Syrian people. The natural resources of Syria belong to the Syrian people," the ministry said.
US Senator Lindsey Graham, a longtime supporter of the YPG/PKK, told Congress on Thursday that he had spoken to YPG-led SDF commander General Mazloum Abdi about the deal.
Asked by Graham if the US was supportive of the deal, Secretary of State Mike Pompeo said: "We are."
The US support for YPG in Syria has become one of the stumbling blocks in bilateral ties between the two NATO allies.
The Turkish military has launched three cross-border into Syria to fight Daesh/ISIS terrorists and the YPG/PKK militants.
The PKK is a designated terrorist organization in Turkey and US, but Washington has refrained from similarly labeling its Syrian cousin as it continues to rely heavily on the YPG as its primary partner in northeastern Syria despite Ankara's objections.
In its more than 30-year terror campaign against Turkey, the PKK -- listed as a terrorist organization by Turkey, US and EU -- has been responsible for the deaths of 40,000 people, including women, children and infants. The YPG is the Syrian offshoot of the PKK.
