NEW YORK -- The leader of a secretive group in upstate New York turned female followers into brainwashed "slaves" who were branded with his initials and coerced into having sex, authorities alleged on Monday in a criminal complaint charging him with sex-trafficking. Keith Raniere, co-founder of the group called Nxivm, was arrested in Mexico and returned to Texas Monday, authorities said. He was to appear in court on Tuesday in Fort Worth on the charges filed by federal prosecutors in Brooklyn.

According to the complaint, Raniere -- known within the group as "Vanguard" -- oversaw a barbaric system in which women were told the best way to advance was to become a "slave" overseen by "masters." They also were expected to have sex with him and do menial chores for masters, and to keep the arrangement a secret or be publicly humiliated, the complaint says.

The name of Raniere's attorney wasn't immediately available on Monday. In a letter attributed to Raniere previously posted on a website related to Nxivm, he denied the practices were sanctioned by the self-described self-help group.

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"These allegations are most disturbing to me as non-violence is one of my most important values," the letter said.

The complaint said that many victims participated in videotaped ceremonies where they were branded in their pelvic area with a symbol featuring Raniere's initials.

"During the branding ceremonies, slaves were required to be fully naked, and the master would order one slave to film while the other held down the slave being branded," the complaint says.

Investigators said Raniere preferred exceptionally thin women, so "slaves" had to stick to very low-calorie diets and document every food they ate. As punishment for not following orders, women were forced to attend classes where they were "forced to wear fake cow udders over their breasts while people called them derogatory names," or threatened with being put in cages, court papers say.

Raniere left the United States late last year after The New York Times reported the stories of some women who defected from their secret sorority and the government began interviewing potential witnesses. He sought to cover this trail by using encrypted email and ditching his phone, court papers say.

He was ultimately found staying with several women in a luxury gated community in Puerta Vallarta where villas can run $10,000 a week to rent, investigators say. After authorities took him into custody on a U.S. warrant, investigators said the women got into a high-speed car chase.

The website related to the group describes Raniere as a "scientist, mathematician, philosopher, entrepreneur, educator, inventor and author" who has "devoted his life to studying the human psychodynamic and developing new tools for human empowerment, expression and ethics."

In a statement on Executive Success Programs website, Nxivm said it "firmly opposes and condemns violence, victimhood, dishonor and abuse."

Nxivm's Mexican affiliate is headed by Emiliano Salinas, a son of that country's former president. Several women who belong to the group in Mexico have traveled to Albany, where they were branded, two former Nxivm members told the Times.

Salinas has also denied that the sorority is affiliated with Nxivm.

Raniere and Nxivm have been the subject of criticism for years, dating back to at least 2012 when the Times Union of Albany published a series of articles examining the organization and allegations that it was like a cult.

Over the years, Nxivm has attracted a following that includes Emmy Award-winning actress Allison Mack. Authorities also say Raniere has been bankrolled by Clare Bronfman, an heiress to the Seagram's liquor fortune.

Bronfman gave millions of dollars covering expenses like private air travel costing $65,000 flight, court papers say.