Turkish President Recep Tayyip Erdogan on Saturday said Turkey and Russia would jointly produce S-500 defence systems after Ankara’s controversial purchase of the S-400 missile defence system from Moscow. Turkey’s push to buy the S-400s has further strained already tense relations with the United States which has repeatedly warned Ankara of the risks including sanctions as a result of the purchase. “There is absolutely no question of (Turkey) taking a step back from the S-400s purchase. That is a done deal,” Erdogan said in Istanbul. “There will be joint production of the S-500 after the S-400,” Erdogan told an audience of young people asking questions.