HAVANA, Cuba (CNN) -- Fidel Castro announced his resignation as president of Cuba and commander-in-chief of Cuba's military on Tuesday, according to a letter published in the state-run newspaper, Granma.

Castro, 81, temporarily handed power to his younger brother Raul Castro in July 2006 after undergoing intestinal surgery. He hasn't been seen in public since his surgery, but he has appeared in numerous videos and photos in state media.

The announcement of Castro's resignation appeared just before 3 a.m. on the Web site of the state-run newspaper.

The news is likely to send shock waves across the island and through the tens of thousands of Cuban exiles who have sought refugee in the United States.

In December 2007, a Cuban television news anchor read a letter reportedly written by Fidel Castro promising he would not "cling to office" or be an impediment to rising young leaders.

Castro took power in Cuba in 1959 and has ruled the island nation ever since, governing the first communist nation in the Western Hemisphere.

Fidel Castro captured the world's attention and imagination at 32 when the bearded revolutionary led a band of guerillas that overthrew a corrupt dictatorship -- and then became an irritating thorn in Washington's paw by embracing communism and cozying up to the Soviet Union.

For the next 47 years, Castro reigned in Havana with an iron hand, outlasting nine American presidents and defying a punishing U.S. economic embargo designed to dislodge him.

Raul Castro is generally seen as more pragmatic and less inclined to deliver the kind of long-winded speeches for which his brother is famous.

Ordinary Cubans have wondered whether a permanent change in power in Cuba will lead to lower food prices, higher salaries and more freedom to travel.