The European Union, EU has asked British aid group Oxfam to explain its handling of a sexual misconduct scandal involving its staff paying prostitutes in Haiti after the devastating quake in 2010.
Oxfam has denied covering up the scandal, which triggered the resignation of its deputy chief executive on Monday.
Oxfam said that they were "grateful" for the actress and her devotion to the charity in the last few years.
"I am nothing short of horrified by the allegations against Oxfam International".
"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".
Roland van Hauwermeiren, 68, was investigated by the charity Merlin, now part of Save The Children, after allegations about his sexual behaviour in wartorn Liberia in 2004.
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Oxfam toughened up how sex abuse allegations among volunteers, both in the United Kingdom and overseas, are investigated after the shocking case when senior staff members hired prostitutes, who may have been underage, for a "Caligula-style orgy" in earthquake-torn Haiti in 2011, as revealed by a damning report.
Oxfam said that with 10,000 NGOs working in Haiti alone in 2011, "it was unfortunately not possible for Oxfam to ensure that those found guilty of sexual misconduct were not re-employed in the sector".
Scotland's global development minister, Alasdair Allan, has held crisis talks with Oxfam seeking assurances that projects involving the Scottish Government are not caught up in the charity's prostitution scandal.
Another involved an assault on a teenage volunteer by a staff member in a charity shop in Britain, she said.
Talking about how charities receiving United Kingdom aid have been told to show "full transparency", Penny Mordaunt said: "If our standards are not met, then the British taxpayer will not continue to fund them".
An Oxfam store in London.
"We expect Oxfam to fully clarify the allegations with maximum transparency as a matter of urgency, and we're ready to review and, if needed, cease funding to any partner who is not living up to the required high ethical standards", spokeswoman Maja Kocijancic told reporters. Plus, the worldwide chairman of the charity has been arrested for corruption.