Turkey has once again defied US calls to abandon a deal for the purchase of Russian S-400 missile defense systems, repeating an offer for a NATO-led working group to resolve the long-running dispute with Washington.

Turkey is set to test its Russian S-400 defense missile system despite repeated warnings from Washington that it could lead to sanctions, Turkish media report.

Turkey has dismissed reports alleging that Ankara is considering delay in the delivery of advanced Russian built S-400 air defense missile systems in the wake of US pressure and threats of imposing sanctions over the purchase of the military hardware, emphasizing the plan is going on as planned.

Turkey on Wednesday reiterated that there will be no delay in the delivery of Russian S-400 air defense systems, an issue which has mounted tensions with the U.S.

Turkish President Recep Tayyip Erdogan said Tuesday at a defense industry fair that a multinational project on the development of the F-35 Lightning II would collapse without Turkey taking part in it.

Turkish President Recep Tayyip Erdogan has reiterated his country’s resolve to proceed with a purchase of advanced S-400 air defense missile system from Russia, a day after an informal deadline Washington set for Ankara to respond to a rival US offer passed.