HAVANA (CNN) -- The young boy at the center of the latest U.S.-Cuban
                  immigration dispute turns 6 on Monday as U.S. officials prepared for
                  new demonstrations outside their compound in Havana.

                  Members of Cuba's Communist Youth group demonstrated outside
                  the U.S. Interests Section in Havana on Sunday to protest the decision to
                  keep Elian Gonzalez with relatives in the United States despite his Cuban
                  father's request that the boy be returned to him. Earlier Sunday, Cuban
                  President Fidel Castro has demanded that U.S. officials turn over the boy
                  by Wednesday or face massive protests.

                  Castro compared the case to a kidnapping and told Cuban state television,
                  "That is not to be negotiated. The right of a father to his son is not for negotiation."

                  U.S. officials ignored Castro's demands Sunday.

                  "We do not respond to press reports of alleged threats being made by Fidel
                  Castro," said a State Department official. But one administration official,
                  who declined to be identified, told CNN the United States has beefed up
                  security around the Interests Section, Washington's unofficial embassy in
                  Cuba.

                  The dispute comes as the United States and Cuba prepare for a December
                  13 meeting to discuss migration between the two nations.

                  Elian was found clinging to an inner tube in the waters off Fort
                  Lauderdale, Florida on Thanksgiving. He was one of three survivors when a
                  boat smuggling Cubans to Florida sank, leaving 10 aboard -- including
                  his mother and stepfather -- to drown.

                  His father, Juan Miguel Gonzalez, wants the boy returned to him. But
                  Elian's relatives in Miami, backed by anti-Castro groups, insist he should
                  stay and enjoy the freedom they say he would not have at home.

                  "All they've done is use the boy as a political weapon against Cuba," his
                  father said.

                  In Havana, speakers at a fiercely anti-American rally denounced "Yankee
                  imperialism" and proclaimed that Cuba's 11 million people were prepared to
                  shed blood to see the boy returned. The hour-long event was closely
                  controlled by Cuban security agents, and there was no attempt to enter the
                  fortified U.S. mission.

                         Correspondent Marina Kolbe and Reuters contributed to this report.