Havana - As Cuba prepared to officially commemorate 50 years of socialism later Thursday, President Raul Castro declared that socialism had "not failed in any way."

In a radio address, the younger brother of Fidel Castro, the father of the Cuban revolution who is too ill to appear in public at any celebrations, disputed remarks by the "enemy ... that socialism has been a failure."

"Why don't they let us in peace to fight for equal conditions? (Socialism) has not been any failure at all," said Raul Castro in a rare interview aired by Cuban television Wednesday night.

Cubans are ready to "resist" all the difficulties, the president declared.

"We have a trained population, over 70 per cent of our population was born during the (US) embargo. If there is a country trained to resist situations like this, it is ours," said Castro, who called for Cubans to "continue" resisting the "imperialism" of the United States.

"These past 50 years have been heroic, we must be proud of all we have endured, we can't let up, we have to continue because imperialism persists," added Raul Castro.

The Cuban president warned of future challenges, like the "vital" question of "developing domestic production," though he insisted he was "proud" and "optimistic." Cuba imports 85 per cent of its food, for example.

"We have always been optimistic, even in the worst moments. We learned that from Fidel," said Castro, who is to speak later Thursday at the main celebrations in the southern Cuban city of Santiago de Cuba, where the iconic Fidel proclaimed the triumph of the Cuban revolution on January 1, 1959.

Fidel Castro, 82, has not been seen by the Cuban public since he fell ill in July 2006, although periodic videotapes of Fidel meeting with other Latin American leaders have been released.

The historic Cuban leader, who resigned definetely from power in February 2008, sent a short message "to the heroic Cuban people" published Thursday on front pages across Cuba.

During his convalescence, Fidel Castro has published almost 200 editorials in the Cuban media. The last photos released of Fidel showed him meeting with Russian President Dmitri Medvedev, who visited Cuba end of November. (dpa)