In an interview with Kanal 24 television late Wednesday, Erdogan also said Turkey could consider purchasing the more advanced Russian S-500 system in the future.
This week, the top US military commander for Europe, Gen. Curtis Scaparrotti, told the US Congress that NATO member Turkey should reconsider its plan to buy the S-400 from Russia or forfeit other future American military aircraft and systems. He said Turkey's use of the Russian surface-to-air missile defense system would be a threat to the F-35.
It was the latest in a series of warnings the US has made to Turkey over its plans to buy the S-400. The US and other NATO allies have repeatedly complained about the purchase, saying it is not compatible with other allied systems and would represent a security threat.
The issue has aggravated already souring relations with Ankara, including tensions over the war in Syria.
"The S-400 is a done deal, there can be no turning back. We have reached an agreement with the Russians," Erdogan said. "We will move toward a joint production. Perhaps after the S-400, we will go for the S-500", AP reported.
The US had agreed to sell 100 of its latest, fifth-generation F-35 fighters to Turkey, and has so far delivered two of the aircraft. But Congress last year ordered a delay in future deliveries.
In December, the State Department approved the sale of a $3.5 billion US Patriot missile defense system to Turkey.
Erdogan said Turkey could still purchase the Patriot system "if the conditions are suitable, the prices are suitable (and) if we can conduct a joint production."
Erdogan added that first delivery of the S-400 would be made in July.