Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. US Slams Turkey for S-400 Tests, Warns of 'Serious Consequences' Jeff Seldin WASHINGTON - Tensions between the United States and Turkey appear to be growing, following the latest war of words between the two allies over Ankara's purchase of Russia's S-400 air defense system. The latest spat ignited Friday, after Turkish President Recep Tayyip Erdogan confirmed earlier reports that Turkey has started testing the Russian-made system, brushing aside U.S. concerns. "(The tests) have been and are being conducted," Erdogan told reporters. "The United States' stance absolutely does not concern us." "If we are not going to test these capabilities at our disposal, then what are we going to do?" he added. .