The 81-year-old handed over power temporarily to his brother Raul in July 2006 when he underwent surgery and has not been seen in public since then. Cuba's new parliament will meet on Sunday to elect a new president.
Washington has called for Cuba to hold free elections, and said its decades-long embargo would remain. "This should be a period of democratic transition for the people of Cuba," said President George W Bush, who also said the US was ready to help the "people of Cuba realise the blessings of liberty". A senior US state department official, John Negroponte, added that the 1962 embargo would probably not be lifted "any time soon".
The European Union said it hoped to relaunch ties with Cuba that were almost completely frozen under Mr Castro, while China described Mr Castro as an old friend and said it would maintain co-operation with Cuba.