Top-secret US military files have revealed that an American aircraft encountered a metallic triangular UFO at around 25,000ft over the eastern Mediterranean, between Greece and Turkey, during a flight back to base, according to newly declassified documents. The incident, logged at an altitude of 24,989ft and a speed of 168 knots, was formally recorded as an unidentified flying object and locked under a 'Secret/NOFORN' classification, barring it …