Fidel Castro's announcement that he was temporarily ceding presidential powers to his brother Raul ushered in a period of uncertainty at home and celebrations by his enemies abroad, while fueling speculation on just how sick he is. The announcement that Castro had been operated on to repair a "sharp intestinal crisis with sustained bleeding" stunned Cubans on the island and in exile, and marked the first time that Castro, two weeks away from his 80th birthday, had relinquished power in 47 years of absolute rule. The news came Monday night in a statement read live on state television by his secretary Carlos Valenciaga. Castro did not appear on the broadcast. Defense Minister Raul Castro, who turned 75 in June and who has assumed a more public profile in recent weeks, also did not appear on television and made no statement of his own. Holding several No. 2 posts in Cuba's power structure, Raul has been the successor for decades. Castro, who took control of Cuba in 1959, resisted repeated US attempts to oust him and survived communism's demise elsewhere, said he was handing over the presidency and the leadership of Cuba's Communist Party to Raul in a move of "provisional character." The elder Castro's message said he had suffered gastrointestinal bleeding, apparently due to stress from a heavy travel and work schedule during recent trips to Argentina and eastern Cuba. Castro last appeared in public on Wednesday as he marked the 53rd anniversary of his July 26 barracks assault that launched the revolution. The Cuban leader seemed thinner than usual and somewhat weary that day during long speeches in the eastern Cuban cities of Bayamo and Holguin. "The operation obligates me to undertake several weeks of rest," Castro's letter read. Extreme stress "had provoked in me a sharp intestinal crisis with sustained bleeding that obligated me to undergo a complicated surgical procedure." It was unknown when or where the surgery took place, as well as where Castro was recovering. Ongoing intestinal bleeding can be serious and potentially life-threatening, said Dr. Stephen Hanauer, gastroenterology chief at the University of Chicago hospitals. The calm delivery of Monday's announcement appeared to signal that there would be an orderly succession to Raul should Fidel become permanently incapacitated. But Fidel seemed optimistic about recovery, asking that celebrations scheduled for his 80th birthday on August 13 be postponed until December 2, the 50th anniversary of Cuba's Revolutionary Armed Forces. While Castro's enemies in exiles celebrated on the streets of Miami, there was no unusual activity on Havana's streets overnight Tuesday as Cubans awaited more word on Castro's condition. The messages streaming across the electronic news ticker at the oceanfront US Interests Section provided a clue something dramatic had occurred inside Cuba's government. "All Cubans, including those under the dictatorship, can count on our help and support," read one message from the American mission. "We respect the wishes of all Cubans." In power since the triumph of the Cuban revolution on Jan. 1, 1959, Castro has been the world's longest-ruling head of government and his ironclad rule has ensured Cuba's place among the world's five remaining communist countries, along with China, Vietnam, Laos and North Korea. Waiters at a popular cafe in Old Havana were momentarily stunned by the news, but quickly returned to work. "He'll get better, without a doubt," said Agustin Lopez, 40. "There are really good doctors here, and he's extremely strong." In another nearby plaza, Cuban musicians kept playing for foreign tourists at outdoor cafes. Signs on the plaza's colonial buildings put up during the recent Cuban holiday said, "Live on Fidel, for 80 more." Martha Beatriz Roque, a leading Cuban government opponent in Havana, said she believed Castro must be gravely ill to have stepped aside - even temporarily. "No one knows if he'll even be alive Dec. 2 when he's supposed to celebrate his birthday," Roque said in a telephone interview. She said opposition members worried they could be targeted for repression during a government change - especially if authorities fear civil unrest. In Washington, White House spokesman Peter Watkins said US authorities were monitoring the situation. "We can't speculate on Castro's health, but we continue to work for the day of Cuba's freedom," he said. Across the Florida Straits in Miami, exiles waved Cuban flags on Little Havana's Calle Ocho, shouting "Cuba! Cuba! Cuba!" as drivers honked their horns. Over nearly five decades, hundreds of thousands of Cubans have fled Castro's rule, many of them settling in Miami. Castro rose to power after the armed revolution he led drove out then-dictator Fulgencio Batista. The United States was the first country to recognize Castro, but radical economic reforms - including the seizure of American property and businesses - prompted Washington to slap a trade embargo on the island and sever diplomatic ties. Cuban revolutionaries opened 10,000 new schools, erased illiteracy, and built a universal health care system. But former liberties were whittled away, independent newspapers were shut down, and religious institutions were harassed. Castro resisted US demands for multiparty elections and an open economy and insisted his socialist system would long outlive him. Fidel Castro Ruz was born in eastern Cuba, where his Spanish immigrant father ran a prosperous plantation. His official birthday is Aug. 13, 1926, although some say he was born a year later. Talk of Castro's mortality was taboo until June 23, 2001, when he fainted during a speech in the sun. Although Castro quickly recovered, many Cubans understood for the first time that their leader would eventually die. Castro shattered a kneecap and broke an arm when he fell after a speech on Oct. 20, 2004, but laughed off rumors about his health, most recently a 2005 report he had Parkinson's disease. "They have tried to kill me off so many times," Castro said late last year about the Parkinson's report, adding he felt "better than ever." But the Cuban president also said he would not insist on remaining in power if he ever became too sick to lead: "I'll call the (Communist) Party and tell them I don't feel I'm in condition...that please, someone take over the command."