Last week, Turkish President Recep Tayip Erdogan confirmed that Turkey had tested the S-400 system on October 16, conducting a missile launch close to the Black Sea city of Sinop.

NATO has repeatedly said that Turkey’s use of the S-400 risks breaching the alliance's operational security. In August, a Greek F-16 fighter jet was reportedly tracked by Turkey using the S-400’s radar system.

Turkey has “become increasingly more self-confident… coupled with a rising element of aggressive rhetoric, a confrontational attitude and the revisionist political position,” Voice of America cited Panagiotopoulos as saying.

"If nothing is done, then Turkey has all the right to believe and its leaders have all the right to believe that they can go on uninhibited, demonstrating that type of hostile and confrontational behavior that threatens stability in the whole region," Panagiotopoulos said.

Turkey took delivery of the S-400 system from Russia in July 2019, leading the United States to remove Turkey from its next-generation F-35 fighter jet program. But U.S. President Donald Trump has thus far resisted calls to impose sanctions on Turkey over the dispute.

"At some point, something needs to be done," Panagiotopoulos said. “Unfortunately, this entails elements of being unpleasant."

Reporter’s code: 50101