Mr Castro, who has not appeared in public since he underwent intestinal surgery in late July, issued a statement saying that he was too sick to attend that was read out to 5,000 supporters that the packed the Karl Marx theatre in Havana.

The ailing Cuban leader's birthday was on August 13, but he postponed celebrations after handing over power temporarily to his brother Raul.

Questions about whether Mr Castro would be well enough to appear have dominated the run-up to the celebrations, leading some guests to say it felt more like a farewell.

The firebrand who seized power in a 1959 revolution could still make a brief appearance at the closing event - a military parade in Havana's Revolution Square on Saturday.

But, after the release of a video on October 28 showing Mr Castro looking gaunt and unsteady on his feet, many Cubans believe he is too old and too ill to resume official duties.

Most Cubans agree that a successor government led by his brother is firmly in place. Government sources say the acting president has been very active holding dozens of meetings, strengthening the ruling Communist Party and coming to grips with Cuba's economic problems.

Mr Castro's statement read out yesterday said: "I direct myself to you, intellectuals and prestigious personalities of the world, with a dilemma. I could not meet with you in a small locale, only in the Karl Marx Theatre where all the visitors would fit, and I was not yet in condition, according to the doctors, to face such a colossal encounter.

"My very close friends, who have done me the honour of visiting our country, I sign off with the great pain of not having been able to personally give thanks and hugs to each and every one of you."

Presidents Evo Morales of Bolivia and Rene Preval of Haiti are due to attend the celebrations this week, along with the former Ecuadorean President Rodrigo Borja and Daniel Ortega, the Nicaraguan President-elect.

Also expected are the Argentinian football hero Diego Maradona and Adolfo Perez Esquivel, an Argentine human rights campaigner and Nobel Peace Prize winner.

Other birthday activities include a three-day academic conference starting today, a concert with Cuban and other Latin American artists on Friday night, and an art exhibit.

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