Turkish President Tayyip Erdogan confirmed on Friday that
Turkey had been testing the S-400 air defence systems that it bought from
Russia and said U.S. objections on the issue did not matter.
Washington says Ankara's purchase of the
Russian systems compromises
NATO defences, and has threatened
sanctions.
An apparent firing test of S-400s test last week prompted a furious response from the U.S. State Department and the
Pentagon.