ANKARA, July 12 (Xinhua) -- Turkish Defense Minister Hulusi Akar held a phone conversation with acting U.S. Defense Secretary Mark Esper late Friday night following the first shipment of Russian S-400 missile defense system in Turkey.

"Turkey's acquisition of Russian S-400 defense system was not a preference but necessity. Evaluations on the proposal of Patriot defense system are still going on," Akar was quoted by Anadolu Agency as saying.

Akar said Turkey's stance on F-35 fighter jets did not change and the country has fulfilled all of its obligations so far.

"Deterioration of Turkish-U.S. ties serves neither Turkey, the U.S. nor the NATO," he added.

Three cargo aircrafts carrying components of Russian S-400 missile defense systems arrived at the Murted Air Base in the Turkish capital Ankara on Friday.

This process will continue in the coming days, Akar told reporters earlier Friday.

Washington repeatedly warned Ankara it will cut off Turkey's purchase of F-35 fighters if Ankara goes ahead with the delivery of the S-400s.

While Turkish President Recep Tayyip Erdogan insisted that it is "a done deal" and his country will not step back "no matter what the consequences will be."