HAVANA (BBC) -- Cuban President Fidel Castro has missed a massive military parade held in his honor in Havana, fuelling more speculation about his health.

President Castro, 80, had emergency intestinal surgery at the end of July and has not been seen in public since.

The parade marked the 50th anniversary of Fidel Castro's return from exile. His younger brother, Raul Castro, Cuba's acting leader, led the events.

He attacked the U.S. but also renewed an offer to hold talks with Washington.

Until the last minute no-one knew if Fidel Castro would make an appearance at the parade, held as part of belated birthday celebrations for him and to mark this key date in Cuban history.

The events began with Raul Castro riding on a jeep through Havana's main square after a 21-gun salute before he launched into a speech praising the Cuban revolution.

He attacked Washington but also left open the possibility of improving ties.

"We take this opportunity to once again state that we are willing to resolve at the negotiating table the longstanding dispute between the United States and Cuba ... as long as the said resolution is based on the principle of equality, reciprocity, non-interference and mutual respect," he said.

The BBC's Stephen Gibbs in Havana says it is significant that Raul Castro used such an event to repeat this, something Fidel Castro would never have done.

Raul Castro gave no further information on the state of his brother's health, which is a state secret.

"Long live Fidel! Long live a free Cuba!," he concluded in front of a crowd of thousands of Cubans.

It had been thought that President Castro might take the opportunity to make his first public appearance in four months on such a significant date.

Exactly 50 years ago to the day, Castro made another comeback, returning to Cuba from exile in Mexico to launch a guerrilla war aided by Ernesto "Che" Guevara.

Three years later, their 9,000-strong force overthrew the regime of Fulgencio Batista.

Soviet-era tanks and missile launchers were on show in Havana's Revolution Square.

Soldiers marched past and a replica of the Granma, the yacht that carried Fidel Castro back from exile, was pulled along the street.

Senior Cuban government figures say that speculation about the Cuban leader's health is ill-informed and spread by his enemies.

But President Castro's non-appearance will increase doubts that he will resume control, correspondents say - a development that would be life-altering news for Cubans, most of whom know no other leader.

Birthday celebrations were initially scheduled when the Cuban leader turned 80 in August, but were moved to December after he became ill.