The U.S. State Department says it has warned Turkey over its potential purchase of a Russian air defense system.
State Department spokesman Robert Palladino said on March 5 that Washington might reconsider giving Turkey access to the advanced F-35 fighter jet program if it buys the Russian S-400 system.
"We've clearly warned Turkey that its potential acquisition of the S-400 will result in a reassessment of Turkey's participation in the F-35 program and risk other potential future arm transfers to Turkey," Palladino said.
The comments were echoed earlier on March 5 by the head of U.S. European Command, General Curtis Scaparrotti, in comments to the Senate Armed Services Committee.
"It presents a problem to all of our aircraft, but specifically the F-35," Scaparrotti told the committee.
The U.S. had agreed to sell 100 of its latest, fifth-generation F-35 fighters to Turkey, but has so far delivered only two of the aircraft.
Congress last year ordered a delay in future deliveries.
Washington has also said it could withdraw an offer to sell Turkey the U.S. missile defense equivalent: the Patriot anti-missile defense system.
Russia media reported last month that Turkey intended to buy four S-400 units for a price of $2.5 billion.
NATO and U.S. officials fear that Turkey's acquisition of the Russian system could allow it to gain access to classified NATO technologies.
United States Warns Turkey Again Over Purchase Of Russian Air Defense System