"It is out of the question for us to revoke the S-400 deal", the Turkish leader said during an interview with TV24 television broadcast late Wednesday. "Such an immoral act would not suit us".
But recent moves by the country to deepen ties with Russian Federation have raised concerns among USA lawmakers.
Turkey's Defence Minister Hulusi Akar told state-owned Anadolu news agency that the move followed an agreement made in September a year ago.
"This is a system that the Turkish government wants, and we want to give it".
The Pentagon is also seeking to install a multinational force in a planned Syria safe zone over Turkey's objections.
Turkey, a North Atlantic Treaty Organisation ally, plans to buy Russia's S-400 long-range air defense system, but the United States has been trying to convince the nation to buy a Patriot air defense system instead.
"My best military advice would be that we don't then follow through with the F-35, flying it or working with allies that are working with Russian systems, particularly air defense systems", Army Gen. Curtis Scaparrotti said Tuesday. At risk for the United States is the delivery of the aircraft to other allies in the consortium, which could face significant delays if Turkey were cut out, due to its role in production.
By adding the S-400s to its military inventory, Turkey aims to protect its airspace from potential threats and heighten border security by modernizing its defense infrastructure.
North Atlantic Treaty Organisation member Turkey intends to proceed with the purchase of the S-400 missile despite US warnings and the sale of the American-made system, claiming it will grant the United States personnel access to the Kremlin weapon. "We are stuck between the two", he said.
Following up, acting Pentagon press secretary Charlie Summers told reporters Friday that "if Turkey takes the S-400, there would be grave effect in terms of our military relationship".
"God willing, we will receive the first system in July".
The comments come as part of this week's back-and-forth between Ankara and Washington on the issue. The jets have spearheaded Turkey's air operations against Kurdish fighters in Iraq and Syria.
"We can't say "yes" to giving control of the safe zone to anyone but Turkey", Erdogan said.