Some people wept among the stunned audience in Santa Clara

Mr Castro is in a plaster cast after three hours of surgery for fractures to his left knee and right arm, suffered during his fall at a rally.

He told Cubans he had refused a general anaesthetic because he could not abandon his duties as head of state.

Venezuela's leftist leader, Hugo Chavez, has sent him his best wishes.

Speaking to supporters in the Venezuelan capital, Caracas, the former paratrooper said his Cuban counterpart had made light of the incident when they talked by telephone.

"I think I would have made a good parachutist," Mr Castro, 78, was quoted as saying.

Correspondents say that the fall revives questions about who, or what, will eventually replace "Fidel", who has ruled with an iron grip since the revolution.

'Little concern'

The US state department appeared to be in no mood to show sympathy for a Communist revolutionary who has defied Washington's power for more than four decades and who has reportedly survived hundreds of assassination attempts.

The leader looked well just before his speech

Asked if the state department wished him a speedy recovery, spokesman Richard Boucher simply replied: "No".

"The situation of Mr Castro is little concern to us but, unfortunately, of enormous importance to the people of Cuba, who have suffered very long under his rule," he said.

One unnamed state department official quoted by AFP news agency in Washington quipped: "We've been looking forward to Castro's fall for years but this isn't what we had in mind."

Mr Castro, whose fall after a speech at a graduation ceremony in Santa Clara on Wednesday night was caught on camera, issued a public letter reporting the surgery he had undergone.

"Given the current circumstances, it was necessary to avoid general anaesthesia to be in conditions to attend numerous important affairs [of state]," he said.