HAVANA (CNN) -- Cubans demonstrated for a second day on Monday
                  to demand that the United States return a Cuban boy rescued off the coast
                  of Florida last month.

                  Elian Gonzalez, who was found clinging to an inner tube on November 25,
                  turned 6 years old Monday and is now staying with relatives in Miami.

                  In Elian's hometown of Cardenas, schoolmates held a birthday party for him
                  at his school, while hundreds of women and children marched in support of
                  his return. Other public demonstrations were held across Cuba and a second
                  mass rally was scheduled for Monday evening outside the U.S. mission in
                  Havana.

                  Elian's mother and stepfather were among those who died when their boat
                  capsized as they tried to reach Florida from Cuba. A total of 11 people died
                  in the crossing. Elian's father, Juan Miguel Gonzalez, 31, is in Cuba and
                  wants his son back.

                  Gonzalez said the boy, who lived with him, was taken out of Cuba by the boy's
                  mother without his permission.

                  "Elian has told me that he misses me, that he wants to return. He cannot be
                  happy there," said Gonzalez.

                  He said he won't go to Miami to exercise his presumed legal right as
                  next-of-kin to pick up Elian. "They have to send him back, that's my right,"
                  Gonzalez said.

                  Castro gives an ultimatum

                  On Sunday, about 500 Communist Youth members demonstrated in front of
                  the U.S. Interests Section, Washington's unofficial embassy in Havana.

                  President Fidel Castro has given the United States until Wednesday to return
                  Elian to his father or face a massive public protest in Cuba.

                  "If they are halfway intelligent, they will announce the return of this child
                  before 72 hours," Castro said Sunday in a speech.

                  If the boy isn't returned, he said, "there will be millions in the street asking for
                  the boy's freedom, and it will not stop until the boy is returned."

                  U.S. law allows any Cuban reaching the shore of the United States to stay.
                  However, in many U.S. child custody cases in which one parent dies,
                  custody is granted to the surviving parent.

                   'No one believes this show'

                   Castro said the matter was not open to negotiation.

                  "The right of a father to his son is not negotiation. One does not negotiate
                  either with corrupt and mercenary judges like the judges from Florida," he
                  said. "The father is asking for the child and the U.S. is keeping the boy
                  kidnapped."

                  Cuban National Assembly President Ricardo Alarcon said that if the boy
                  isn't reunited with his father, Cuba would boycott a December 13 meeting
                  on the implementation of migration accords with the United States.

                  A U.S. State Department official said the Clinton administration does not
                  respond to threats.

                  "We do not respond to press reports of alleged threats being made by Fidel
                  Castro," he said.

                  The official said the United States has tried not to "politicize" the issue and
                  believes the matter should be settled in the courts.

                  U.S. Rep. Ileana Ros-Lehtinen (R-Florida) said Castro's threats should not
                  be taken seriously.

                  "I think these are empty threats of Fidel Castro. He says that if we don't act
                  within 72 hours, he will have a million people demonstrating in Cuba. Well,
                  so what?" she said. "So he has 1 million or 3 million ... no one believes this
                  show."