"What is the concern or claim? That F-35s and S-400s are not compatible ... And here is our proposal, let me remind you or repeat: let's establish a working group and NATO can chair or lead this, and let them, let the experts examine this, asses this," Cavusoglu said at a session on NATO's future.
"We believe that they are not incompatible," the minister added.
The United States has repeatedly objected to Ankara’s purchase of the Russian-made defence system, saying that the weapons system is incompatible with NATO security standards. Ankara insists that the S-400 systems would not pose a threat for the alliance and resisted US pressure to cancel orders.