"There is an agreement. We have determination. It is out of the question to take a step back from it [S-400 deal]," Erdogan told reporters in Istanbul.
Turkey decided in 2017 to purchase the S-400 system following protracted efforts to purchase air defense systems from the U.S. with no success.
However, U.S. officials have advised Turkey to buy the Patriot missile system rather than the S-400 system from Moscow, arguing it is incompatible with NATO systems.
Turkey has responded that it was the U.S. refusal to sell it Patriots that led it to seek other sellers, adding Russia offered it a better deal, including technology transfers.
"We can take a step for Patriots, if there is a positive offer as Russia made," Erdogan said, adding but so far there was no positive offer from the U.S. side.
Erdogan added win-win approach is in the self-interest of every country. "If it is not the case, we are not obliged to buy anything."
The S-400 is Russia’s most advanced long-range anti-aircraft missile system and can carry three types of missiles capable of destroying targets, including ballistic and cruise missiles.
It can track and engage up to 300 targets at the same time and has an altitude ceiling of 27 kilometers (17 miles).