A Patriot missile unit at the Defense Ministry in Tokyo, Japan, October 8, 2017. (file photo)

ANKARA, March 1 (Xinhua) -- Turkey is negotiating with the United States about the purchase of U.S. Patriot missile defense systems, Turkish Foreign Minister Mevlut Cavusoglu said on Friday.

During an interview with local broadcaster, Cavusoglu said that Ankara had received a positive response from Washington to its last letter sent nearly two years ago about the purchase.

Turkey has important considerations about the cost, delivery schedule and technology transfer in the future, the minister said.

"While Turkey hopes to secure the purchase of the Patriot systems, it can also turn to other options if negotiations with the U.S. do not turn out in its favour," he added.

U.S. officials warned earlier that if Turkey proceeds with the Russia's S-400 purchase, Washington would withdraw its offer to sell a 3.5-billion-U.S.-dollar Patriot missile package, and could block the sale of fighter jets to Turkey and impose sanctions.

Cavusoglu reiterated that the S-400 deal is a done deal and the system would be delivered in the fall.