In a statement Castro said he wouldn't seek a new presidential term when Cuba's National Assembly meets on February 24.

The 81-year-old has been suffering from an undisclosed illness, and its severity has never been established.

He has appeared in pictures and video but hasn't been seen in public for more than a year and a half.

His departure raises doubts about the future of the West's only communist state.

Castro's brother Raul has run Cuba as acting president since July 2006 and is expected to be named successor.

Even after stepping down Fidel Castro's position as first secretary of Cuba's communist party means he'll remain influential in the country he's shaped.