Turkish F-16 warplanes will fly over the countrys capital Ankara on Monday to test its new Russian S-400 missile defenses, Turkish media said, despite pressure from Washington for Turkey to drop the system. Ankaras purchase of the S-400s and its subsequent delivery in July has been a major source of friction with the United States, which says the system is not compatible with NATO defenses and poses a threat to Lockheed Martins F-35 stealth fighter jets. The provincial governors office announced on Sunday that the Turkish Air Force F-16s and other aircraft will conduct low- and high-altitude flights over Ankara on Monday and Tuesday to test an air defense system project. Broadcaster CNN Turk and other media said specifically that the flights were to test the S-400 radar system. Dealers said the reports had a negative impact on the lira, which weakened to 5.7380 against the dollar from a close of 5.7140 on Friday. Tensions in US-Turkish relations played a major role in a near 30 percent slide in the liras value last year. As recently as last Thursday, a senior State Department official told reporters Turkey needed to "get rid of" the system. Those comments came after President Tayyip Erdogan met US President Donald Trump at the White House. Trump said afterwards that Turkeys controversial acquisition created "serious challenges" for Washington as he added officials would "immediately" get to work on resolving the issue. Washington has suspended Turkey from the F-35 program, which it was a buyer and producer of, to punish it for the S-400 purchase. It has warned of possible US sanctions over the deal but has not yet imposed them. Trump has told Erdogan that Washington is ready to sell Ankara US Patriot systems if it drops the Russian system.