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-Turkey Tensions Escalate Over Russian Missiles Dorian Jones ISTANBUL - Turkey's Defense Minister Hulusi Akar dismissed the Pentagon's latest warning over Ankara's imminent procurement of Russian missiles on Thursday as "language unbecoming of an ally." U.S. acting Secretary of Defense Patrick Shanahan's letter to his Turkish counterpart laid out a detailed timetable of Turkey's exclusion from the purchase and production of America's latest F-35 fighter jet if Ankara buys Russia's S-400 missiles system. The Pentagon claims the S-400 would compromise the F-35 and, in particular, its stealth technology that was developed to evade systems like the S-400. .