An heiress pleaded guilty on Friday in a sensational case accusing a cult-like upstate New York group of creating a secret harem of sex slaves for the group's self-anointed spiritual leader.

Clare Bronfman admitted in her plea in federal court in Brooklyn that she harboured someone who was living in the US illegally for unpaid "labour and services" and that she committed credit card fraud on behalf of Keith Raniere, the lead of a group called NXIVM.