Cuba's former President Fidel Castro (R), Bolivia's President Evo Morales (C) and Venezuela's President Nicolas Maduro sit together in a van in Havana, Cuba, August 13, 2015. [Photo/Agencies]

That is one of several conditions Washington must meet to fully normalize relations between the two countries, Cuba has maintained, including lifting the trade embargo and withdrawing from Guantanamo Bay, where the US operates a naval base and notorious prison.

Fidel, who has not opposed the restoration of ties, but said early on that he did not trust the US, also asserts "we will never stop struggling for peace and the well-being of all human beings, for every inhabitant on the planet regardless of skin color or national origin, and for the full right of all to hold a religious belief or not."

He included a birthday wish. "The equal right of all citizens to health, education, work, food, security, culture, science, and well-being, that is, the same rights we proclaimed when we began our struggle ... is what I wish for all."

Venezuela's President Maduro congratulated Fidel in a series of posts via Twitter, and posted photos of the historic figure with the late Venezuelan leader Hugo Chavez, a close friend and political ally until his death from cancer in 2013, as well as with Che Guevara and Camilo Cienfuegos.

"Congratulations Fidel ... the struggle continues," wrote Maduro in one post.

In Biran, Fidel's birthplace, military cadets planted 100 cedar trees in his honor, and more than 400 members of youth organizations took part in cultural performances and presentations throughout Wednesday night, singing "Happy Birthday Comandante" at the first light of Thursday.