The BBC said South African police took custody of the three so-called blood diamonds last week.
"If these stones are the proceeds of conflict in West Africa, they should be converted into money which can be used for the benefit of the victims of the 11-year civil war in Sierra Leone," said Yasmin Jusu-Sheriff, Sierra Leone human rights commissioner.
Taylor is on trial by the war crimes tribune in The Hague. He is accused of giving rebels in Sierra Leone weapons in exchange for diamonds. Taylor denies the charges.
Campbell, best known as a fashion model, testified at the trial she received the diamonds after a 1997 dinner. Other witnesses said they were a gift from Taylor.