Turkish President Recep Tayyip Erdoğan said Tuesday he hoped the United States’ approach towards Turkey’s purchase of the Russian S-400 missile defense system would change, Reuters reported.

US and NATO officials have told Ankara that the Russian system cannot be integrated into the NATO air and missile defense system and that purchasing the S-400 system would jeopardize Turkey’s purchase of Lockheed Martin Corp F-35 fighter jets and possibly result in US sanctions.

“Relevant institutions are conducting necessary talks right now,” Erdoğan told Turkish broadcaster NTV. “They will continue to do so. They will also speak to Congress. I hope that this wrong approach [of the US] will change.”