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

The resignation ends nearly a half-century of iron-fisted rule that inspired revolutionaries but frustrated 10 U.S. presidents.

Castro revealed his plans without notice by publishing a letter in the middle of the night in state-run newspaper Granma.

"I will not aspire to, nor will I accept the position of president of the council of state and commander in chief," Castro wrote. "I wish only to fight as a soldier of ideas. … Perhaps my voice will be heard."

President Bush said Castro's decision ought to spark "a democratic transition" for Cuba.

"The international community should work with the Cuban people to begin to build institutions that are necessary for democracy and eventually this transition ought to lead to free and fair elections," Bush said Tuesday in Rwanda. "The United States will help the people of Cuba realize the blessings of liberty."