Turkish President Recep Tayyip Erdogan says Turkey continues to make payments under a deal with Russia to purchase advanced S-400 air defense missile systems, which Washington has warned could put Ankara at risk of US sanctions.

“The S-400 holds an important place in our talks. The United States’ arguments are very wrong. We finished the S-400 process and our payments continue,” Erdogan told reporters in Istanbul on Friday.

He emphasized that the United States had not presented the same terms when it offered to sell Patriot missiles.

Russian presidential aide Yury Ushakov told reporters in Moscow on Friday that the delivery of S-400 systems from Russia to Turkey may be on the agenda in a meeting between Russian President Vladimir Putin and his Turkish counterpart next week.

Turkish Foreign Minister Mevlut Cavusoglu said on Thursday that the purchase is a “done deal” and cannot be cancelled.