The State Department has already authorized a $3.5 billions sale of the Patriot missile system to Turkey, but officials say Ankara will not receive it unless they ditch their deal with Russian Federation.
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 an interview with broadcaster Kanal 24, Erdogan said it would be "immoral" for Turkey to turn back from its deal with Russian Federation.
Ankara has said it has already paid the bulk of the price for the S-400s and that the systems are expected to arrive in November.
The S-400 remains "a problem to all of our aircraft, but specifically the F-35", Gen. Curtis Scaparrotti told the Senate Armed Services Committee on Wednesday arguing that the United States should stop the stealth fighter transfer to Turkey and "forfeit" sales of other military technology to its North Atlantic Treaty Organisation ally, if Ankara deploys the Russian-made defensive weaponry as expected in July. Last month, President Recep Tayyip said that Ankara was not satisfied with U.S. reluctance to provide Turkey with a loan needed to buy the PAC-3, or to organise joint production of the air defence system.
Turkey's decision to buy Russia's S-400 air defence system does not mean that it's rejecting the US' Patriots, Turkish Vice President Fuat Oktay has said.
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Turkey has invested more than US$1.25 billion in the stealth F-35 jet since its development phase began in 2002.
North Atlantic Treaty Organisation member Turkey has repeatedly said it is committed to buying the Russian missile defence system, despite warnings from the United States that the S-400s can not be integrated into the North Atlantic Treaty Organisation air defence system.
The same day, US European Command chief Gen. Curtis Scaparrotti told lawmakers from the Senate Armed Services Committee that he didn't recommend delivering F-35s to Turkey if it didn't abort its S-400 deal with Russian Federation.
"We're not a slave, we're independent", Erdogan said.