Turkey bought S-400 missile defense systems from Russia to use them, not put them aside, the head of the Turkish Defense Industry Directorate said on Saturday, days after talks between President Recep Tayyip Erdogan and US President Donald Trump. Erdogan and Trump held talks in Washington on Wednesday to overcome increasing differences between the NATO allies, ranging from Syria policy to sanctions threats over Turkey’s purchase of the S-400s, which Washington says pose a threat to its Lockheed Martin F-35 fighter jets. Washington has warned that Ankara will face sanctions over its purchase of the S-400s, and has suspended Turkey from the F-35 program, in which it was a customer and manufacturer. It has yet to impose any sanctions on Turkey, which began receiving the Russian systems in July. In an interview with broadcaster CNN Turk, Ismail Demir said it was not logical for any country to purchase such systems only to put them aside, and added that Ankara and Washington aimed to tackle the issue. “It is not a correct approach to say ‘we won’t use them for their sake’ about a system that we bought out of necessity and paid so much money for,” Demir said, according to Reuters. “We have allied relations with Russia and the United States. We have to go on and respect the agreements we signed,” he said. On Wednesday, Trump urged Erdogan at the White House to drop the S-400 systems, but Erdogan later said Ankara could not harm its relations with Russia. He reiterated Turkey’s desire to buy US Patriot defenses in addition to the S-400s. A top aide to Erdogan said on Friday that Turkish and US officials had begun working as part of a joint mechanism aiming to evaluate the impact of the S-400s on the F-35s. Demir said the move showed an easing in the position of the United States, and added that Turkey was ready to take measures that will address US concerns over the S-400s after the talks. “As a loyal friend and ally, we have said we were ready to take measures if there are any risks that we have overlooked on this issue,” Demir said. “We still believe we can find a middle ground on the S-400 issue, so long as both sides are open.” He also said Turkish personnel were continuing their training on the S-400s in Russia, but added that there would be no Russian personnel coming to Turkey to operate the systems.