Masked men stole stuffed rhinoceros heads containing eight valuable horns from the warehouse of Ireland's National Museum, police and museum officials said Thursday, in a heist being linked to an Irish Gypsy gang that specializes in such raids across Europe.

Police said three men raided the storeroom in Swords, north of Dublin, on Wednesday night and tied up the lone security guard. He later freed himself and raised the alarm.

Nigel Monaghan, keeper at the National Museum's natural history section, said the museum had never experienced such a theft before but had worried that the rhinos would be targeted. He said the four heads — three of black rhinos from Kenya, one of the virtually extinct white rhino from Sudan, all killed more than a century ago — were removed from display last year and put into storage specifically to safeguard them from thieves.