A U.S. fighter jet shot down a Turkish drone armed with air-to-surface missiles that was flying extensively in the area of U.S. ground troops in northeast Syria on Thursday, according to a U.S. official. An F-16 shot the drone down after a dozen unheeded calls to Turkish military officials stating American forces were in the area and the U.S. would engage in self-defense if it didn't leave, according to the official. The shootdown of the Turkish drone comes days after Turkey conducted retaliatory airstrikes in northern Iraq against locations related to the outlawed Kurdish Workers Party (PKK), the militant Kurdish...