“We continue to stress at the highest levels that the S-400 transaction is the subject of ongoing CAATSA sanctions deliberations and it remains a major obstacle in the bilateral relationship and at NATO. We are confident that President Erdogan and his senior officials understand our position,” U.S. State Department spokeswoman Morgan Ortagus said on Monday.

Following Turkeys' acquiring of Russian S-400 missile system, the United States decided to end the F-35 before July 31, 2019.

Acting Defense Secretary Patrick M. Shanahan had warned Turkey that such a deal with Russia risks undermining its ties to NATO. The United States threatened Turkey with CAATSA sanctions over Turkey's decision to buy the S-400 missile defense system from Russia.

President Trump's administration officials including Secretary of State Michael Pompeo and former National Security Adviser John Bolton move on with the sanctions.

On 22 July 2019, Turkey claimed to retaliate against the “unacceptable” threat of US sanctions over Turkey’s purchase of Russian S-400 missile defenses. (ILKHA)