London (CNN)Actress Minnie Driver is stepping down as one of Oxfam's global ambassadors following revelations of sexual abuse by aid workers in Haiti.
Driver is the first celebrity spokesperson to abandon the charity amid the growing scandal, which includes allegations that Oxfam staff used sex workers in Chad.
"I am nothing short of horrified by the allegations against Oxfam International. In no uncertain terms do I plan to continue my support of this organization or its leaders. And though it is unfortunate that after 20 years I am no longer able to advocate and defend through this specific framework, social and economic injustice is more globally prevalent than ever," she said in a statement Tuesday.
"I certainly will not let the abhorrent mistakes of a troubling organization stop me or anyone else from working with good people in this space to support a population of human beings around the world that needs our help."
Former deputy chief executive Penny Lawrence resigned Monday as the scandal continued to grow.
Oxfam's leaders are accused of trying to cover up the behavior of some of its senior staff members deployed to Haiti after the devastating 2010 earthquake. Aid workers, including the Oxfam country director at the time, Roland van Hauwermeiren, were accused of turning a villa rented by the organization into a makeshift brothel, with prostitutes wearing only Oxfam T-shirts.
Oxfam has apologized for the behavior of aid workers, but denies a coverup.
Oxfam International Executive Director Winnie Byanyima said the charity is not where it needs to be. But she said it's "much better" than it was in 2011 and it will continue to rebuild.
"I know that Oxfam will recover because there are a few people who have abused the power that they had ... and abused the very people they were meant to protect. But the majority, the thousands of Oxfam staff around the world are saving lives," Byanyima told CNN's Hala Gorani.
"They are risking their lives every hour and this is good work that we will continue to do."
Byanyima said abuse of power was a problem throughout humanitarian aid work and urged international groups to start sharing information. She said change would only come from a "systemwide" response, and pledged that Oxfam would "lead our sector" in instituting stronger accountability measures.
"I am deeply hurt at what happened to those women in Haiti and I feel for them, I want justice for them and we have sent our regional director to Haiti to explore and see what we need to do for justice to be done."
In a statement Tuesday, Oxfam thanked Driver for her service and reiterated its commitment to accountability.
"Minnie Driver has been a devoted Oxfam supporter for many years, and we are grateful for her commitment to ending global poverty. Her decision to step down as an Oxfam ambassador saddens us deeply, but we also understand and respect her choice.
"As an organization, we are ashamed by the actions of some of our staff and are more committed now than ever to learn from our mistakes and ensure we uphold the highest levels of safeguarding standards in our work around the world."