Ailing Cuban leader Fidel Castro told hundreds of admirers who traveled here for his 80th birthday party that he was not well enough to meet with them on Tuesday.

In a written message read at the launch of his five-day birthday bash, Castro said his doctors told him he was not in condition to attend the kickoff Tuesday night at Havana's Karl Marx Theater.

"I direct myself to you, intellectuals and prestigious personalities of the world, with a dilemma," said the note read at the gathering and broadcast live on state television.

"I could not meet with you in a small locale, only in the Karl Marx Theater where all the visitors would fit and I was not yet in condition, according to the doctors, to face such a colossal encounter," it added.

The crowd responded by giving Castro a standing ovation.

"My very close friends who have done me the honor 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," Castro wrote.

The Cuban leader has been seen by the public only in photos and videos since his July 31 announcement that he was temporarily ceding power to his brother, 75-year-old Defense Minister Raul Castro, while he recovered from surgery for intestinal bleeding. Details of his ailment and his medical treatment are state secrets.

U.S. government officials said earlier this month there is still some mystery about Castro's diagnosis, his treatment and how he is responding. But the officials believe he has terminal cancer of the stomach, colon or pancreas.

More than 1,300 politicians, artists and intellectuals from around the globe were expected to pay homage to the man who governed the communist-run island for 47 years.

Presidents Evo Morales of Bolivia and Rene Preval of Haiti have confirmed they will attend the celebrations along with former Ecuadorean President Rodrigo Borja and Nicaraguan President-elect Daniel Ortega.

Also expected are Colombian Nobel laureate Gabriel Garcia Marquez and Nobel Peace Prize winner Adolfo Perez Esquivel, an Argentine human rights activist.

Noticeably absent will be Castro's good friend and political ally Venezuelan President Hugo Chavez, who is up for re-election Dec. 3. In his absence, Chavez promised to dedicate his electoral victory to Castro.

The festivities were originally scheduled around Castro's actual birthday on Aug. 13. After falling ill, Castro asked to postpone them to Dec. 2 to coincide with the 50th anniversary of the founding of Cuba's Revolutionary Armed Forces.

Other events planned for the celebration include the dedication of the new San Geronimo College, a three-day academic conference, a concert, an art exhibit and a parade Saturday expected to draw 300,000 people.