Turkey's Russian air defence systems and U.S. response

FILE PHOTO: A view shows a new S-400 "Triumph" surface-to-air missile system after its deployment at a military base outside the town of Gvardeysk near Kaliningrad, Russia March 11, 2019. REUTERS/Vitaly Nevar//File Photo

(Reuters) - Turkish President Tayyip Erdogan this week flagged potential further cooperation with Russia on defence industry projects including fighter jets and submarines even as the United States warned it could respond with more sanctions.

Turkey received the first deliveries of the S-400 surface-to-air systems in July 2019, prompting Washington to begin removing the NATO ally from its F-35 stealth fighter programme over security concerns.