The United States has imposed a fresh round of sanctions on Cuba, targeting among others the state company that imports the spare parts keeping the island's collapsing power grid alive, even as daily blackouts in parts of the country now stretch beyond 24 hours.The US Treasury's Office of Foreign Assets Control designated six Cuban targets on September 3, the Associated Press reported. They include Abapet, the Oil Industry Supply Import Company, which brings in the specialised equipment and replacement parts needed to maintain Cuba's thermal power plants. Also designated were Fidel Ernesto Castro, grandson of former president Raúl Castro, state…