Regardless, Erdogan said he and Vladimir Putin, the Russian president, "are determined on this issue," according to Harriyet.
Erdogan also lashed out at those questioning Turkey buying a Russian air defense system and suggested Ankara would make its own decisions on what to buy, regardless of NATO's wishes.
"It's us who will make decisions regarding our independence," the Turkish president said. "We are responsible over taking security measures for defense of our country. We'll save ourselves if we face difficulties in procuring defense systems."
Turkey, a NATO member since 1952, reportedly sees the Russian technology transfer as a national priority to grow its indigenous defense industry, and U.S. missile defense makers maybe less willing to part with valuable intellectual property. Yet it also raises questions about the long-term aims of Turkey since the S-400 is seen as not interoperable with similar NATO hardware.
"It is up to Allies to decide what military they will buy," NATO spokesman Mark Sanders told CNBC in an email statement. "What matters for NATO is that the equipment Allies acquire is able to operate together. Interoperability of our armed forces is fundamental to NATO for the conduct of our operations and missions."
That said, Sanders indicated that "no NATO ally currently operates the S-400. NATO has not been informed about the details of any purchase."
To be clear, Turkey has looked to buy air defense systems from U.S. rivals in the past, although it then reversed course after pressure was applied.
Back in 2015, Turkey looked set to acquire China's export version of the FD-2000 long-range air defense missile system for $3.4 billion but backed out after pressure from NATO. Also, the Chinese reportedly refused to budge on all of the Ankara government's technology transfer demands.
Still, the S-400 deal sends a signal to Washington that Turkey, a longtime NATO member, could down the road change its position on Incirlik Air Base, home to U.S. warplanes and nuclear gravity bombs. Also, it raises questions as Turkey is scheduled next year to get its first of 100 F-35 stealth fighter jets and share in the technology of this advanced fighter.
"The list of American concerns about Turkish policies and behavior is rather extensive," Steven Cook, a senior fellow for Middle East and Africa studies at the Council on Foreign Relations, testified last week before the Senate Committee on Foreign Relations. He said they include not only the Russian S-400 equipment but "threats to rescind American access to Ircirlik," among other things.
Turkey is angered by the U.S. alliance with the YPG-led Syrian Democratic forces to defeat ISIS. The Kurdish YPG militia (or People's Protection Units) are a branch of the outlawed terrorist group Kurdistan Workers' Party (or PKK).
"Ankara rightly considers this group to be inextricably linked to the PKK," Cook testified. "More than any other issue, the U.S. relationship with the YPG through the Syrian Democratic Forces has driven tension in American-Turkish ties."
Meantime, Erdogan also fumed to reporters about the cost to buy drones from allies. "They give tanks, cannons and armored vehicles to the terror organization but we can't procure some of our needs, although we want to pay the price. What happened in the end? We started to produce our own drones and armed drones."
But Michael, the Pentagon spokesman, sought to downplay any rift with Ankara in his statement. "Turkey is a key NATO Ally, and we are committed to our strong defense partnership," he said.
Moreover, the Pentagon official said there remains "a robust and significant defense-trade and military-sales relationship" between the two countries.
"Turkey continues to pursue anti-missile systems from NATO Allies, including the U.S., for its broader, long-term missile defense needs," Michael said. "The United States is committed to expediting the delivery of equipment purchased by Turkey, when possible."
Read the full report from Hurriyet.