FILE PHOTO: Sukhoi Su-35 jet fighters of the "Sokoly Rossii" (Falcons of Russia) aerobatic team fly in formation during a rehearsal for the airshow in Krasnoyarsk, Russia August 1, 2019. REUTERS/Ilya Naymushin

MOSCOW (Reuters) - Russia and Turkey are holding talks about the possible sale of Russian-made Sukhoi SU-35 fighter jets to Turkey, but it is too early to talk about a concrete deal, RIA news agency cited a senior Russian official as saying on Friday.

Turkey has been at odds with the United States over its purchase of Russian S-400 missile systems, which Washington says are not compatible with NATO defenses and poses a threat to Lockheed Martin’s F-35 ‘stealth’ fighter jets.

The United States has also expelled Turkey from the F-35 program, but Ankara has so far dismissed the warnings.