Oxfam's deputy chief executive has resigned over the scandal of its workers abusing sex workers in Haiti.
Penny Lawrence, who was the charity's international programmes director when the alleged sexual abuse happened, stood down on Monday, saying: "I am ashamed that this happened on my watch and I take full responsibility."
She is the first resignation from the charity after days of bad headlines about its staff using sex workers, some of whom may have been underage, while working in the country after the devastating 2010 earthquake.
She said Oxfam had "failed to adequately act on reports" of its country director in Chad using sex workers, which he was accused of before he moved to Haiti.
Lawrence added: "Over the last few days we have become aware that concerns were raised about the behaviour of staff in Chad as well as Haiti that we failed to adequately act upon.
"It is now clear that these allegations - involving the use of prostitutes and which related to behaviour of both the Country Director and members of his team in Chad - were raised before he moved to Haiti.
"As programme director at the time, I am ashamed that this happened on my watch and I take full responsibility.
"I am desperately sorry for the harm and distress that this has caused to Oxfam's supporters, the wider development sector and most of all the vulnerable people who trusted us."
Oxfam chief executive Mark Goldring: "I deeply respect Penny's decision to accept personal responsibility.
"Like us, she is appalled at what happened and is determined to do what is best for Oxfam and the people we exist to help."
Lawrence was international programmes director from 2006 to 2014, when she became deputy chief executive.
She added: "It has been such a privilege to work for such an amazing organisation that has done and needs to continue to do such good in the world."