HAVANA (Reuters) -- The eldest son of Cuban leader Fidel Castro said on Monday his father is recovering from an unspecified illness that has forced him to temporarily give up power he held since a 1959 communist revolution.

But Fidel Castro Diaz-Balart, better known in Cuba as "Fidelito," did not answer when asked if his father would be well enough to attend a Dec. 2 public celebration of his 80th birthday.

"The only thing I can tell you is that he is recovering," the younger Castro told Reuters before quickly walking away.

"Fidelito" Castro, who is 57 and a nuclear physicist, spoke to Reuters at a biotechnology conference in Havana.

Father Fidel Castro turned 80 on Aug. 13, but he was not well enough to take part in a public celebration and said it should be put off until Dec. 2, when Cuba celebrates the start of the revolution that put him power.

Recently, Cuban officials have said it was not known if Castro will be able to attend the event, saying it depends on his condition.

His brother Raul, who has been defense minister since 1959, has been in charge of the government since Castro's surgery, announced on July 31.