Tensions between the US and Cuba over the custody of the boy mounted after Havana also demanded the return of six Cubans said to have hijacked a boat to Florida. Washington insists the fate of the boy should be left to the courts - US courts. The row now threatens the most bitter political crisis in US-Cuban relations for a decade.
Elian was rescued by US coastguards off southern Florida on 25 November, and was entrusted to relatives in Miami. He had been found clinging to an inner tube, after his mother and stepfather drowned when their refugee boat capsized in a storm. They were trying to escape to America.
The timing of the rescue, on Thanksgiving Day, and the child's winning looks combined with the constant tensions in the US-Cuba relationship to propel him to celebrity status in Florida's Cuban emigre community. There, his fate is seen as a symbol for the right of Cubans to free themselves from Fidel Castro's communist regime. With presidential and congressional elections only a year away, no politician can ignore the growing political clout of the state's Hispanic voters.
But the boy, who celebrated his sixth birthday in Miami on Monday, immediately became a symbol in Cuba, too, for the lengths to which US "imperialism" is prepared to go to impose its ideology and values on others.
Elian's natural father and both sets of grandparents launched pleas - relayed on Cuban television - for his immediate return to the land of his birth. His father accused his ex-wife of taking the child out of the country illegally; the Cuban authorities accused the United States of "kidnapping".
On Monday, as Elian was feted by his relatives in Miami - most of them recent emigres from Cuba - Mr Castro visited the boy's school in the town of Cardenas. His teachers had organised another birthday party so his classmates could lament his absence and demand his return.
Mr Castro promised them: "Little Elian will get back his country, his family, his school, his schoolmates, his school desk." The child was designated a "boy hero of Cuba" and his picture was plastered in the school and on the streets.
Elian's father, Juan Miguel Gonzalez, and other relatives were shown on television calling Elian by phone to wish him a happy birthday. "Are you coming back soon," his father asked. "Yes," said a timid voice from afar. "Tell my classmates to take care of my things."
In Miami, Elian had a birthday cake topped with a toy helicopter and two miniature fighter planes. His presents included a red bicycle, and accoutrements for the emigre passion - a baseball, a baseball glove and a bat.
In Washington, US officials have taken an increasingly firm line on Elian's case. After remaining mute for days, in the apparent hope that the case would be settled without overt official intervention, the State Department and the White House issued statements on Monday with statements insisting that Elian would not be sent back against his will. They rejected Fidel Castro's ultimatum and said the boy's future should be determined first by the immigration service, and then, if necessary, by the courts.
They also reminded the Cuban authorities that they had a legal responsibility to ensure the safety of the 50 or so US diplomats stationed in Havana. Impassioned demonstrations have been staged outside the mission and at the father's home in Cardenas.
The militantly anti-Castro Cuban emigre community in Miami is adamant that the boy should not be returned, but American opinion seems divided between those who think family ties are paramount and those who believe the "miracle boy' survivor should be able to benefit from his good fortune in surviving the shipwreck.
There is also division in US official circles between those who believe a low-key approach would bring the best results, and those who see the child's fate as a test of US determination to stand up for principle.
Some believe the Cuban authorities deliberately escalated the dispute to balance what was seen as an insult to Fidel Castro, who had wanted to attend the World Trade Organisation meeting in Seattle last week, but was strongly discouraged by the US.
With formal talks on ensuring the orderly flow of migrants from Cuba just a week away, Cuba also has an interest in taking a firm line. Mr Castro has already threatened to cancel the talks because of Elian, a move that could precipitate another mass exodus from Cuba of just the sort the current emigration rules are designed to pre-empt.