The President said in an accompanying statement that he felt “very happy”, but the wording of the text gave the impression that he was far less optimistic than his aides that he would return to work.

“To say the objective stability (of my health) has improved considerably is not to invent a lie,” he said in a typically convoluted passage. “(But) to say that the recovery period will last little and that there is no risk would be absolutely incorrect.”

Señor Castro, apparently preparing Cubans for a life without him, said that they should remain optimistic while being “ready to face any bad news”. “The country is marching on and will continue marching on perfectly well,” he said.

More than 70 per cent of Cubans have known no other leader.

Yesterday’s pictures showed him in an adidas tracksuit bearing the Cuban colours, looking slightly fatigued. In one, he is holding up a telephone; in another, a copy of yesterday’s official newspaper, apparently to dispel any doubts about whether he was alive. Rumours that the Cuban Government has been covering up his death have been sparked by his failure to appear since his operation for intestinal bleeding two weeks ago.

However, a handwritten statement to five Cubans jailed for espionage in the United States looked spidery and weak. The Cubans’ appeal was overturned by a US court last week. “We will defeat this monstrous injustice!” he wrote in a shaky hand.

On the eve of his birthday, many Cubans chanted “Long live Fidel” at a five-hour concert by Havana’s famous sea-wall, the Malecón.

Señor Castro’s birthday was to be the occasion of a three-day jamboree with thousands of foreign admirers flying in to praise him and the revolution he spawned. The celebrations have been postponed until December.

Señor Castro’s closest international ally, President Chávez of Venezuala, flew to Havana yesterday and was greeted by his brother, Raúl. It was the first time the younger Castro had been seen in public since becoming interim president on July 31.

Before leaving Caracas, Señor Chávez said of Señor Castro, who is famous for five-hour speeches: “This morning he was very well. He is up from his bed and talking more than he should.”

President Morales of Bolivia, who has formed close ties with Cuba and Venezuela, sang “happy birthday, commandante” to Señor Castro yesterday. He said that in December he would take him a birthday cake made with coca leaves.

Venezuela has been propping up Cuba’s economy with nearly 100,000 barrels a day of cut-price oil and petroleum products, amid a host of other benefits.

Cubans perplexed about who is in charge of their country will have received little in the way of solid new information. Until they know whether Señor Castro is going to return to power or not, few Cubans, even avowed opponents, would risk moving against him.

But those attuned to reading between the lines of Cuba’s official statements detect a campaign to prepare the people for an orderly succession of power.

When he was taken ill, the Cuban leader temporarily handed most — but not all — of his functions to Raúl, 75. He gave responsibility for his pet programmes to younger ministers and placed the Communist Party in charge of the ideological direction of the Government. Raúl and the official news agencies have repeatedly said that the party, not Raúl, would wield power after Fidel.

Analysts believe that Fidel Castro has set the stage for a more collective style of leadership after 47 years of autocratic rule in an effort to ensure that his revolution outlives him. But some Cuban political analysts believe that, without his brother’s charisma or emotional hold over Cubans, Raúl would be forced to grant them new freedoms.

Fidel’s personal charisma has repeatedly allowed him to survive periods of mounting social pressure. In 1994, during the depths of the economic slump caused by the Soviet Union’s collapse, there were angry riots by frustrated youths hurling bricks and stones. The Cuban leader arrived on the scene and dived into the crowd, which changed mood and began chanting “Fidel! Fidel!”.

He also allowed Cubans to leave for a limited time, releasing some of the pressure against his regime. An estimated 30,000 crossed the Strait of Florida to the US in boats and rafts. Neither Raúl nor any other party apparatchiks would command that sort of authority. They would most likely have to allow Cubans to travel abroad and, perhaps, conduct their own business.

Raúl has travelled to China and some think he would emulate its approach of allowing economic opening while retaining tight political control.

Portrait of a revolutionary

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