Police said that a 6-year-old boy kidnapped Tuesday by masked men in a working-class neighborhood of the Puerto Rican capital appeared hours later apparently unharmed.

The boy, identified as Alfry Infante Perez, was dropped off in front of the island's Ombudsman's Office in San Juan, where he was taken in by a security guard who called police, said police spokesman Roberto Diaz.

"The boy looked to be in good health," he said in a phone interview. "He only complained about being hungry."

Doctors will examine the boy, while police are still investigating what motivated the kidnapping, Diaz said. No one has been arrested.

The four assailants had fled with the child in a grey Jeep Cherokee, according to the FBI, which took over the investigation because it has jurisdiction over kidnapping cases in Puerto Rico, said Special Agent Maritza Conde Vazquez, a spokeswoman for the agency in the U.S. island territory.

Conde declined to comment on a possible motive.

Puerto Rico police said in a statement that the boy was with his father, who was injured in the attack. It occurred in Barrio Obrero, a neighborhood of San Juan.

Local newspaper El Vocero reported that the father had been kidnapped last year and was rescued by the FBI. Conde declined to comment on the report.