Following years of allegations that she fabricated details about her own back story as well as those of supposed sexual assault victims, Somaly Mam, Cambodia’s most famous anti-sex-trafficking activist, has resigned from the global fundraising organisation that bears her name.

The high-profile resignation, announced yesterday by Somaly Mam Foundation (SMF) executive director Gina Reiss-Wilchins, sent shockwaves through the cluster of anti-trafficking organisations in Cambodia, and came just days after Newsweek published a damning indictment of her life’s work.

“We have accepted Somaly’s resignation effective immediately,” Reiss-Wilchins says in the statement. She adds that the decision was made after a two-month probe commissioned by the organisation. It does not mention the Newsweek article or previous media coverage about Mam that first raised questions about her past.

The foundation hired law firm Goodwin Proctor LLP in March to conduct the investigation into the claims against Mam and alleged trafficking victim Long Pros, whom the organisation had used in media campaigns to attract support and funding. Pros’s story turned out to be a cobbled-together version of other peoples’ experiences.

“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,” the statement reads. It adds that the foundation will continue to work with its local affiliate, Agir Pour Les Femmes en Situation Precaire (Afesip), which Mam founded in 1996.

The foundation said Pros – whose harrowing story of being sold to a brothel where she was abused and tortured was brought under the media spotlight by New York Times columnist Nick Kristof and an appearance on Oprah – would also be leaving.

“We are permanently removing Ms Pros from any affiliation with the organisation or our grant partner, but will help her to transition into the next phase of her life,” it said.

Simon Marks’s Newsweek report built on a series of stories he did while working at The Cambodia Daily newspaper.

Mam is also alleged to have fabricated and scripted the testimony of another woman, Meas Ratha, for a French documentary in 1998, which propelled her into the media spotlight and began her journey to celebrity status in the global fight to end sex trafficking.

Moreover, Mam backtracked on a statement she made in 2012 to the UN General Assembly, where she claimed that Cambodian soldiers had killed eight girls in a raid on one of her shelters in Phnom Penh in 2004.

As the SMF grew in prominence, it attracted the backing of Hollywood stars and venture capitalists, public-relations gurus and politicians, which in turn added to its fundraising power.

Anti-trafficking and women’s rights groups in Cambodia yesterday responded to the news of Mam’s resignation with concern.

“I’m quite disappointed in Somaly; it’s already difficult to hear that a woman working on this issue is lying to other women … but what’s even worse is that this culture of victimhood that so many use when talking about survivors of trafficking will only be made worse,” said Ros Sopheap, executive director of rights group Gender and Development for Cambodia.

“I recognise that many women and children have been supported by this organisation but why did she fabricate these lies? These women and girls don’t need more lies in their lives.

“The worst situation would be if donors back out and the women and girls being supported are left behind.”

The SMF did not respond to requests for comment.

Others rallied behind Mam and the work of Afesip and the SMF.

Helen Sworn, founder of NGO Chab Dai, said that the situation was “difficult” but she hoped that “the good work the organisation was doing continued”.

“Somaly’s story needs to be separated from the work carried out by the organisation. I commend her decision to step down,” she said, adding that the group “does incredibly important work that should be at the centre of conversations now”.

Thomas Steinfatt, a professor of statistics at the University of Miami who conducted studies on trafficking figures for the UN’s Inter-Agency Project on Human Trafficking, said that “the lies Somaly tells in her backstory are likely just the tip of the iceberg”.

Steinfatt estimated in 2008 that there were no more than 1,058 trafficking victims in the country, a figure that fell far short of figures quoted in SMF and Afesip promotional material and funding requests.

Annette Lyth, regional manager for the UN Action for Cooperation Against Trafficking in Persons, said that it was “highly unfortunate” that Mam had fabricated some of the stories.

“[Trafficking victims’] realities and their needs have not changed because of this story and we pledge our support to continue supporting victims of trafficking, as do the donors we are sure,” she said.