Somaly Mam had received U.S. government funding for some of her early work and wrote a memoir, "The Road of Lost Innocence," which was a best-seller in France, with a tale of being abused and sold into prostitution as a child, one of several claims that have now been questioned.
Her work has attracted high-profile attention, receiving publicity from journalists such as New York Times columnist Nicholas Kristof and support from celebrities such as actress Susan Sarandon and Facebook executive Sheryl Sandberg. The website of her Somaly Mam Foundation lists as corporate partners cosmetics company Estee Lauder, finance firm Goldman Sachs and Hilton hotels.
A statement issued Wednesday by the foundation's executive-director, Gina Reiss-Wilchins, said Somaly Mam's resignation was accepted after the group was presented with the findings of a two-month investigation it had commissioned from a California-based law firm, Goodwin Procter. Details of the findings were not released.
Somaly Mam could not be reached for comment. Calls to her phone number in Cambodia went unanswered Thursday and her office in Cambodia said it did not know where she was.
"While we are extremely saddened by this news, we remain grateful to Somaly's work over the past two decades and for helping to build a foundation that has served thousands of women and girls, and has raised critical awareness of the nearly 21 million individuals who are currently enslaved today," Reiss-Wilchins said in the statement, which was posted on the foundation's website.
Somaly Mam's resignation followed a cover story in Newsweek which publicized long-questioned aspects of her story. In Cambodia, questions had been raised for several years, especially by the newspaper The Cambodia Daily.
Among the claims that had raised doubts were that her daughter had been kidnapped by traffickers seeking revenge on her, and that eight girls who had been seized from one of her group's refuges in Cambodia in 2004 were murdered by the army there.
Colleagues of Somaly Mam told The Cambodia Daily the daughter had run away from home, and the newspaper reported that she herself retracted the story of the eight murdered girls, which she had related in a speech at the United Nations.
Among those who said she was untruthful were several colleagues and her French ex-husband, Pierre Legros, who helped found her original Cambodia-based organization, AFESIP, which is the French acronym for Acting for Women in Distressing Situations. AFESIP, formed in 1996, says on its website that it operates in Cambodia and neighboring Laos to rescue girls and women from forced prostitution, while the Somaly Mam Foundation acts as its fund-raising arm.
In 2008, Somaly Mam was the co-winner of the $150,000 World's Children's Prize for the Rights of the Child, awarded by the Swedish Children's World Association to recognize those who defend the rights of children. In 2006, she was honored as one of Glamour magazine's women of the year.
Glamour magazine made her story more widely known through a September 2006 article by Mariane Pearl, a journalist and widow of slain Wall Street Journal reporter Daniel Pearl.
"It's one thing to know theoretically that there is child prostitution and really dire conditions in those brothels, but it was shocking," said Pearl, who visited Somaly Mam in Phnom Penh in May that year. "The girls that Somaly introduced me to are babies. ... They needed an ambassador. They needed someone to say, 'OK, this is what's going on.' She has the courage to say that, and without her there's just no voice."
The foundation was founded in 2007. Its announcement on Somaly Mam's resignation said another Cambodian woman staffer whose story had been discredited was being fired.
"Despite our heartfelt disappointment, the work of the Foundation and our grant partners must and will carry on," it said. "We have touched the lives of over 100,000 women and girls. We have treated nearly 6,000 individuals at a free medical clinic in Phnom Penh's red light district and engaged nearly 6,400 students in anti-trafficking activism."
Associated Press writer Grant Peck in Bangkok, Thailand, contributed to this report.