US Secretary of State Mike Pompeo has expressed his displeasure over Turkey’s purchase of Russian S-400 missile defense system – despite Washington’s objection and threat of sanctions – during a phone conversation with his Turkish counterpart Mevlut Cavusoglu.

The development was announced Saturday in an official statement by the US Department of State, which added that Pompeo also discussed Ankara’s “security concerns” along the Turkey-Syria border while reiterating Washington’s “obligation to ensure the protection of local partners working with the United States” in Syria.

Reuters also cited Turkish foreign ministry sources as saying that the two top diplomats also discussed the US F-35 fighter jet program, just two days after Washington confirmed Turkey’s expulsion from the program that involved joint manufacture of the advance war plane and training of Turkish pilots to fly the aircraft.

“The US and other F-35 partners are aligned in this decision to suspend Turkey from the program and initiate the process to formally remove Turkey from the program,” said US Under Secretary Of Defense for Acquisition and Sustainment Ellen Lord last week.