Cuban leader Fidel Castro came close to death in 2006, according to the latest secret US diplomatic cables published by Wikileaks.
Mr Castro almost died after suffering a perforated intestine during an internal flight, unnamed sources told US diplomats in Havana.
The illness led Mr Castro to hand power to his brother Raul, although he has since returned to public life.
The 84-year-old's health is considered a state secret in Cuba.
The Wikileaks cables, published by the Spanish newspaper El Pais, reveal the intense efforts made by US diplomats in Havana to find out the nature of Fidel Castro's illness and his chances of recovery.
The names of the sources of information reported in the cables have been redacted by Wikileaks, but some apparently knew people who were close to the Cuban leader, or had access to his medical records.
The details of what they say cannot be independently verified.
One cable, sent in March 2007 by the then-head of the US interests section in Havana, Michael Parmly, quotes a report by an unnamed doctor on the moment Mr Castro fell seriously ill in July 2006.
"The illness began on the plane from Holguin to Havana," reports the cable.
As it was a short flight there was no doctor on board and they had to land urgently once they knew of Mr Castro's bleeding. He was diagnosed with diverticulitis of the colon.
The source said Mr Castro had a perforation of the large intestine and needed surgery.
But it says he "capriciously" refused to have a colostomy, with the result that his condition deteriorated over time and he required further surgery.
"This illness is not curable and will not, in her opinion, allow him to return to leading Cuba," the report concludes.
"He won't die immediately, but he will progressively lose his faculties and become ever more debilitated until he dies."
Further leaked cables quote other sources as saying Mr Castro was terminally ill, and examine statements by his medical team and reports of specialist drugs being brought into Cuba.
But the reports of his imminent death have proved to be exaggerated.
Mr Castro has since made an apparent recovery and earlier this year returned to making speeches and appearing in public, though he has not taken back the reins of power from his brother Raul.
The former Cuban leader recently praised Wikileaks and its founder, Julian Assange, saying the leaks of thousands of diplomatic cables had brought the US "morally, to its knees".
"Julian Assange, a man who a few months ago hardly anyone in the world had heard of, is showing that the most powerful empire in history can be defied," he wrote in an article published by Cuban state media.
The US government and its intelligence agencies have been staunch enemies of Mr Castro and the communist government in Cuba for more than half a century.
So far, all their predictions of the imminent demise of communist party rule on the island have proved false.