Former self-help guru Keith Raniere goes on trial in New York on charges of running a secretive sex cult that recruited female "slaves" who were then starved, branded with his initials and blackmailed into having sex with him.

Federal prosecutors have charged Mr Raniere, 58, with using his cult like Nxivm group, which claimed to offer members unique insights into life, as a front for crimes including sex trafficking, child pornography and sexual exploitation of a minor.

Several of his alleged "slaves" are expected to testify at US District Court in Brooklyn.

While prosecutors have not said who will take the stand, former 'Smallville' star Allison Mack and Seagram liquor heiress Clare Bronfman have already pleaded guilty to playing supporting roles in the scheme.

Allison Mack starred as Chloe Sullivan in Smallville

Jurors have been warned to expect disturbing testimony and evidence during a trial that could run for six weeks.

Prosecutors intend to introduce explicit photographs of a 15-year-old girl alleged to have been one of Mr Raniere's victims, seized from his computer hard drive.

Mack and Bronfman are among five co-defendants, all women accused of involvement in Nxivm, who pleaded guilty to various charges in March and April, leaving Mr Raniere as the sole person to face trial.

The television actress tearfully acknowledged in court that she had blackmailed two women into providing services for her and other Nxivm members.

Bronfman, who provided key financial support for Nxivm, pleaded guilty in April and agreed to forfeit $6m (€5.35m).

Mr Raniere has pleaded not guilty to all charges.

Marc Agnifilo, one of his lawyers, has said that his client's sexual encounters with women in the organisation were consensual and denied the child pornography and exploitation charges.

The trial caps a bizarre saga for Mr Raniere, who was arrested in March 2018 after fleeing to Mexico with Bronfman.

Nxivm, which started under another name in 1998 and is pronounced "Nexium," was based in Albany, New York, and at one time operated numerous centres across the United States, Canada, Central America and Mexico.

The organisation marketed itself as a business "providing educational tools, coaching and trainings" that would allow "humanity to rise to its noble possibility," according to court filings.

In 2015, prosecutors say, Mr Raniere established a sorority within Nxivm known as DOS, an acronym for a Latin phrase that roughly translates to "master of the obedient female companions".

The subgroup included "slaves" who were expected to bend their wills to "masters" in a pyramid-like structure, with slaves expected in turn to recruit their own subordinates and Mr Raniere standing alone at the top.

The slaves were required to submit "collateral" to win acceptance that could then be used as blackmail material: Nude photos, rights to their financial assets or damaging information about friends and relatives, prosecutors said.

Several women were branded with Mr Raniere's initials, prosecutors said, and they were required to engage in sexual acts with him.

He is also accused of having forced some women to maintain slim figures by following a dangerously restrictive diet.