"As for the S-400, the deal is done and it is out of the question to go backwards. and perhaps after the S-400, we will move onto the S-500", Erdogan told Kanal 24 television.
Army Gen. Curtis Scaparrotti, the senior USA general for operations in Europe and NATO's top officer, warned in congressional testimony this week that Turkey's pursuit of the S-400 deal would jeopardize American plans to sell to Ankara the new F-35 Joint Strike Fighter for both policy and security reasons.
Despite many attempts to purchase the Patriot air defense system from the U.S., Turkey has not been able to achieve this due to conflicts such as the "transfer of technology" issue.
The comments come as part of this week's back-and-forth between Ankara and Washington on the issue.
Washington has also said it could withdraw an offer to sell Turkey the USA missile-defense equivalent - the Patriot anti-missile system. "We may also go into S-500s after the S-400s".
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The US fears the Russian system could be used to collect intelligence on the jet's stealth capabilities, but Erdogan said "we've researched it, there is no such thing". "They will not get the F-35s if they take the S-400".
The US agreed to sell 100 of its F-35 fighters to Turkey in December and has so far delivered two of the aircraft. "In total, F-35 industrial opportunities for Turkish companies are expected to reach $12 billion", according to information posted by Lockheed Martin, the jet's manufacturer.
Summers said those consequences would encompass losing USA military sales to Turkey, including the long-awaited sale of the United States' new F-35 Joint Strike Fighter jet.
Russian Federation has utilised the S-400 system in its military operations in Syria.
Turkey's Defence Minister Hulusi Akar told state-owned Anadolu news agency that the move followed an agreement made in September a year ago. Turkey's plan to buy the S-400 from Russian Federation may make this hard. "God willing, we will receive the first system in July".