"The United States is very concerned about Turkey having our F-35s in proximity to S-400 Russian system because there could be a transfer of information, communications or even interruption of that," Hutchison said on Tuesday. "It's a very serious issue."
Russia and Turkey signed a loan agreement for the supply of S-400 air defence systems in 2017. In early March, Turkish President Recep Tayyip Erdogan reaffirmed that the deal with Russia on deliveries of the S-400 air defence systems was completed, and said a new deal on purchases of advanced Russian-made S-500 systems could be possible in future.
READ MORE: Acting US Defence Chief Expects Turkey to Purchase Patriot Instead of S-400s
A State Department official told Sputnik on Monday that the US government warned Ankara that it could face even more consequences including sanctions for purchasing Russian S-400 systems.