An explosive device carried by a drone exploded on Sunday at the headquarters of Russia’s Black Sea Fleet, injuring six people, officials said. The explosion at the headquarters in the city of Sevastopol on the Crimean peninsula that Russia annexed from Ukraine in 2014 caused the cancellation of the Russian Navy Day holiday. The press service of the Black Sea Fleet said the drone appeared to be improvised. He described the explosive device as “low-powered,” but Sevastopol Mayor Mikhail Razvozaev said six people were injured in the blast. There is no immediate information on where the drone started its flight.