He said in a letter published in online official media that he would not accept a new term when the newly elected parliament meets on Sunday.

"I will not aspire or accept - I repeat I will not aspire or accept, the post of President of the Council of State and Commander in Chief," read the letter.

It was published without advance warning in the online edition of the Communist Party daily Granma.

The new National Assembly is meeting for the first time on Sunday since January elections to pick the governing Council of State, including the presidency Castro holds.

There had been wide speculation about whether he would accept a nomination for re-election to that post or retire.

The 81-year-old Castro's announcement effectively ends his rule of almost 50 years over Cuba, positioning his 76-year-old brother Raul for permanent succession to the presidency.

Castro temporarily ceded his powers to his brother on July 31, 2006, when he announced that he had undergone intestinal surgery.

Since then, the elder Castro has not been seen in public, appearing only sporadically in official photographs and videotapes and publishing dense essays about mostly international themes, as his younger brother has consolidated his rule.

Castro rose to power on New Year's Day 1959 and reshaped Cuba into a communist state 90 miles from US shores.