WASHINGTON (Reuters) -- The CIA has concluded that Cuban President Fidel Castro suffers from Parkinson's disease and could have difficulty coping with the duties of office as his condition worsens, an official said Wednesday.The assessment, completed in recent months, suggests the nonfatal but debilitating disease has progressed far enough to warrant questions among U.S. policymakers about the communist country's future in the next several years."The assessment is that he has the disease and that his condition has progressed. There appear to be more outward signs," said an official who is familiar with the assessment. (Watch: How healthy is Castro? -- 2:17)Bush administration officials and members of Congress have already been briefed on the findings about Castro. The Cuban leader, 79, has been in power on the island of 11 million people since leading a 1959 revolution. He has long been at ideological odds with Washington.But U.S. diplomats played down the significance of any CIA assessment and said they were not using such intelligence to make policy decisions about Castro or Cuba."Do we see him losing his grip over the country? No," said a State Department official, who asked not to be named because he was discussing intelligence conclusions. "We are not in any way adapting how we plan for the day Castro is gone based on an assessment that he might have Parkinson's."The CIA based its assessment on a variety of evidence, including observations of Castro's public appearances and the opinions of doctors employed by the agency."If the assessment is correct, you could expect there to be effects on his ability to come to grips with fresh challenges over the next several years," said the U.S. official who has seen the CIA report. He spoke on condition of anonymity because the document is classified."It could have implications for the way Castro functions, and by natural course, the way the Cuban government functions," the official added.The Rumor MillCuban officials declined to comment on the CIA assessment. They insisted Castro was in good health when he failed to show up at a summit of Ibero-American leaders in Spain in October.Castro has long been the subject of rumors of illnesses, including Parkinson's, despite a generally strong physical constitution. Many of the reports up to now have come from the anti-communist Cuban-American community in Florida.Castro has dismissed them as the work of his enemies who wish to see him dead. In a recent television interview with Argentine soccer star Diego Maradona, Castro joked the rumors were so common that the day he died, nobody would believe it. (Read about Castro's remarks to Maradona)The Cuban leader's pace has slowed noticeably since tumbling to the floor after a speech a year ago. But his stamina appears unabated and he still gives long speeches. (Read about his fall and the State Department reaction)Castro's brother Raul, head of the armed forces, has been designated as his successor and the Cuban leader has said that he expects Cuba's political system to outlive him."If it's true and he does have it, then it's still an open question anyway as to how much it might -- somewhere further in the future -- affect how he runs Cuba. So we would not use this kind of conclusion to inform our policymaking," the State Department official said of the CIA assessment.Cuba and the United States have no diplomatic relations, and Washington imposed an economic embargo on Havana 43 years ago. It is still in effect.Parkinson's is a chronic, irreversible disease that affects about 1 percent of people over the age of 65 worldwide. Among notable sufferers are actor Michael J. Fox, boxing legend Muhammad Ali and former U.S. Attorney General Janet Reno.In October 2004 when Castro tripped and broke his left knee and right arm after a speech, he refused tranquilizers and general anesthetic during a three-hour operation, telling Cubans he was fully in command of government affairs.He has dismissed reports of illnesses ranging from stroke and brain hemorrhage to heart attack and hypertensive encephalopathy. Copyright 2005 Reuters. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.