Cuba's President Raul Castro waves to the crowd during the May Day parade at Havana's Revolution Square May 1, 2008. Raul Castro confirmed he was handing over the leadership of the Cuban Communist Party to a younger generation at its congress that kicked off on Friday, ending six decades of rule by himself and older brother Fidel. REUTERS/Sven Creutzmann/Pool/File Photo

Cuba's President Raul Castro attends to an ALBA alliance summit in Caracas March 17, 2015. In a speech opening the four-day event, Castro, 89, said the new leadership would be party loyalists with decades of experience working their way up the ranks and were "full of passion and anti-imperialist spirit." REUTERS/Carlos Garcia Rawlins/File Photo

Cuban First Secretary of Communist Party Raul Castro Ruz gives a speech, on January 01, 2019, during the celebration of 60th Anniversary of Cuban Revolution at Santa Ifigenia Cemetery in Santiago de Cuba. Castro had said at the previous party congress in 2016 it would be the last one led by the "historic generation" who fought in the Sierra Maestra to topple a U.S.-backed dictator in the 1959 leftist revolution. Yamil Lage/Pool via Reuters/File Photo

Cuban President Raul Castro waves as he arrives to attend a speech from U.S. President Barack Obama at the Gran Teatro in Havana, Cuba, March 22, 2016. The transition comes as Cuba faces the worst economic crisis since the collapse of former benefactor the Soviet Union, while there are signs of growing frustration, especially among younger Cubans. REUTERS/Carlos Barria/File Photo

Cuba's President Raul Castro attends the May Day parade at Havana's Revolution Square May 1, 2008. REUTERS/Sven Creutzmann/Pool/File Photo