Castro's not-unexpected announcement comes just before Sunday's Cuban National Assembly meeting to choose members and president of its Counsel of State. Castro had signaled he would not seek re-election because of his health, making it official in a letter published in Tuesday's editions of Cuban newspapers, The Miami Herald reported.

"It would be a betrayal to my conscience to accept a responsibility requiring more mobility and dedication than I am physically able to offer," the 81-year-old Castro wrote. "This I say devoid of all drama."

His brother, Raul, has been acting ruler of the island nation since Castro "temporarily" named him president in 2006 after falling ill with an intestinal illness. Raul Castro, 76, served as Cuba's defense minister.

Some experts said they thought the Council of State could name Cuban Vice President Carlos Lage, 54, to replace Castro, while others said it would be unlikely both Castros would retire at once, the Herald said.

The Castros swept into power in 1959 after winning a revolution against Gen. Fulgencio Batista.