The United States yesterday rejected Cuba's demand for the return of a 6-year-old boy rescued at sea and told Havana it was obligated to protect U.S. diplomatic personnel there from protesters.

Cubans staged a second day of protests outside the U.S. mission in Havana yesterday to demand the return of Elian Gonzalez, who was found clinging to an inner tube in waters between Cuba and Florida on Nov. 25 after a craft full of people capsized while trying to reach the U.S. coast.

Among the 11 passengers who died was the boy's mother. The boy, who turned 6 yesterday, is staying with his relatives in a large Cuban exile community in Miami while a custody battle takes shape. His father and grandparents in Cuba are demanding his return.

Cuban President Fidel Castro Sunday demanded that the United States return the boy in three days, which the State Department dismissed. "This is not conducive to resolving this case in the appropriate humanitarian way," said State Department spokesman James Foley.

"We are committed to working with the family of the boy, including the father, and all appropriate officials to achieve an appropriate resolution to this case," Foley said.

Washington made clear that the Immigration and Naturalization Service is playing a lead role in determining the fate of the child, and that if a challenge arises to any INS decision, it would be up to a Florida state court to decide.

[Elian's cousin Marisleysis Gonzalez, 22, of Miami, and Lazaro Gonzalez, his great uncle, told Washington Post staff writer Guy Gugliotta that Elian has told his uncle that he doesn't want to go back to Cuba.

["He said he wants to stay here. I don't know if they'll take a 6-year-old's word for that," the cousin said. The family will go to the INS on Dec. 23.

[She said the family is not worried about Castro's threats. "I don't know what he'll be capable of doing," she said. "He's not the father."]

Castro has threatened to cut off talks between the United States and Cuba, scheduled for Dec. 13, that are aimed at ensuring an orderly flow of migrants between the countries. "It's not conducive to resolving this case appropriately to make threats about ending talks," said National Security Council spokesman Mike Hammer.

But of more immediate concern to Washington is the safety of diplomats at the U.S. mission in Havana, where loud anti-American protests have erupted. The United States warned Cuba that it had an international obligation to protect the 50 Americans at the mission.

"We hold the Cuban government responsible for any harm to U.S. citizens or to our interest section that may come from the public protests called for by the Cuban government," said Foley.

White House spokesman Joe Lockhart said, "We will respond appropriately and deal with any serious threat, because of the seriousness of our concern for Americans' safety."