Tens of thousands of protesters gathered in Belgrade on Saturday for a rally against lithium mining in Serbia, despite officials warning of an alleged plot to topple President Aleksander Vucic and his government. Vucic said he was tipped off by Russian intelligence services that a “mass unrest and a coup” were being prepared Saturday by unspecified Western powers that wish to oust him from power. The large crowd chanted: “There Will Be No Mining” and “Treason, Treason.” Some within the crowd marched toward the capital’s two main train stations, saying they would block train traffic until their…