A US actress has appeared in court, charged with recruiting women for an alleged sex cult.

Allison Mack - best known for her role in the TV series 'Smallville' - was arrested yesterday on charges of sex trafficking.

The 35-year-old's accused of involvement with an organisation called Nxivm, which publicises itself as a "self-help group".

But its founder Keith Raniere, who was arrested last month, is alleged to have blackmailed women who joined into becoming sex slaves.

In this courtroom sketch Keith Raniere (second from right), leader of the secretive group NXIVM, attends a court hearing in the Brooklyn borough of New York | Image: Elizabeth Williams/AP/Press Association Images

Prosecutors say he had a "rotating group of 15 to 20 women with whom he maintains sexual relationships", with Mack said to have lured in many of his victims through an internal programme called The Source, which targeted actors to become his "slaves".

She is accused of forcing the women to have sex with Raniere and to take compromising photos of themselves.

Mack was arrested by the FBI after being accused by two women of directing them to engage in sexual activity with Raniere (57) who allegedly gave Mack money and other benefits in return.