Fidel Castro says U.S. owes Cuba millions

In Cuba, the embargo is referred to as "the blockade," considered a decades-old rallying cry against U.S. influence. First implemented in 1960 after the Castro-led government seized U.S.-owned oil refineries, it was strengthened over the next two years. Lifting the embargo against Cuba requires an act of Congress, something President Obama called for in January during his State of the Union address. 

Wednesday's letter coincides with growing talk among anti-Castro groups in the U.S. about American compensation for properties nationalized during the Cuban Revolution. 

The assets of U.S. companies, such as Exxon Mobile and Coca Cola, as well as private properties, were seized during the process of Cuban nationalization in early 1960s, shortly after Fidel Castro and band of Cuban revolutionaries toppled the government of U.S.-backed Fulgencio Batista on January 1, 1959.

Some estimates place the value of those properties at roughly $7 billion, accounting for five decades of accruing interest. The Cuban government has given no indication it is willing to provide compensation, though President Raúl Castro said in April during the Summit of the Americas in Panama that he is willing to discuss "everything."

Castro also said he "will agree to disagree" with Obama when it comes to the intractable issues between the two countries, though he did not elaborate.