0929 GMT March 24, 2019
"That does not represent – far from it – a rejection of peacefully settling conflicts," said the letter, a week after communist Cuba and the United States held landmark talks in Havana as they attempt to normalize ties, AFP said.
US President Barack Obama and Cuban President Raul Castro announced December 17 that the Cold War rivals would work to normalize relations that broke off in 1961.
In Washington, some Cuban-American lawmakers slammed Obama, saying his administration had given up too much without securing human rights commitments from the Americas' only one party communist-ruled country.
Yet what many observers found most stunning in so much change is that the leader of Cuba's 1959 revolution – a lawyer by training famous for speaking for hours in excruciating detail – has yet to publicly speak about the detente that his brother Raul, 83, has engaged with his old enemy.
"Cuba's president has taken steps within his range of authority and the powers granted him by the National Assembly, and the Communist Party of Cuba," the letter attributed to Fidel Castro added.
"We shall always defend cooperation and friendship with all of the world's peoples, among them our political adversaries," the letter dated Monday added.
It did not address swirling rumors of his demise, which have cropped up often since Fidel Castro first took seriously ill in 2006.
With only official state media offering Cuba's 11 million people information, word of mouth can be an influential factor in the economically distressed country's everyday life.