“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, Hurriyet daily reported.

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.”

Erdogan also said Turkey had offered to set up groups with the U.S. to work together on the issue, without saying what Washington’s response had been. Last week a top Pentagon official said the consequences would be “devastating” for Turkey’s joint F-35 fighter programmer and its cooperation with NATO if the country went ahead with plans to buy the Russian anti-aircraft weapon system.

Kathryn Wheelbarger, Acting Assistant Secretary of Defense for International Security Affairs, said the planned purchase would damage Turkey’s ability to work with the Western alliance, and force Washington to hit the country with sanctions against arms deals with Russia.

Last month Turkish Defense Minister Hulusi Akar said the country was already “preparing” for U.S. sanctions.

U.S. officials said they expect Turkey to opt for the American Patriot missiles instead, arguing that would then allow the F-35 program to continue.

Turkey plans to buy 100 US F-35s, and some Turkish pilots have already started training with counterparts in the U.S.

Kremlin spokesman Dmitry Peskov on June 4 said Turkey did not have to warn Russia, when asked if Ankara informed Moscow of its proposal to create a joint working group with Washington.

“Turkey did not have to warn us. This is not our business. Our business and that of our Turkish partners is to conclude the transaction over the delivery of S400s, which is being carried out,” he said.

“Turkey can talk about that with any third country.”

Reporter’s code: 50101