Oxfam's most senior figure is urging victims of abuse to come forward as she promised "justice" and announced an independent commission to "root out" sex offenders.
Winnie Byanyima, Oxfam International's executive director, offered an apology over a sex and prostitution scandal that she described as "a stain" on the charity.
A series of allegations, first published by The Times a week ago, has seen senior Oxfam workers accused of soliciting prostitutes while overseeing aid operations around the world.
The charity has also come under fire for its initial response after concerns about sexual exploitation were raised years ago, although it has denied covering up allegations in Haiti in 2011.
Posting on Twitter, Ms Byanyima said: "I am inviting anyone who has been a victim of abuse to come forward.
"My message to women who have suffered: I'm fighting this abuse. I'm with you. We are going to do justice.
"Oxfam will be a standard bearer of safety and dignity for all who interact with us."
The charity chief has also announced a "high-level independent commission" made up of women's rights experts, to "look into our culture and our practices and make recommendations to make us stronger at protecting our people".
"We are going to root out, we are going to create a vetting system that will help us," she told the BBC.
Ms Byanyima admitted Oxfam has "a problem" but said she "cannot know" how deep the problem of sexual exploitation is within the charity until the independent investigation is complete.
"I know that we have almost 10,000 staff around the world working in more than 90 countries," she said.
"The majority of those are doing the right thing, are people of values who care about humanity, who are saving lives.
"We do have, I know, a porous system that has brought in people who do not share our values and that's my challenge."
Ms Byanyima said Oxfam was "very hurt" but insisted the charity would survive the scandal.
She said: "There is no way this organisation can die. The world needs it."
A former member of Uganda's parliament, Ms Byanyima also offered a guarantee British taxpayers' money and cash from donations would continue to help the world's poor.
"If you just look at the work Oxfam has been doing in the last four years alone, 90 million people we reach every year, and these are people who are desperate, who need help," she said.
Alongside the commission, which will be able to access charity records and interview staff around the world, Ms Byanyima announced a series of reforms within Oxfam.
This includes a new global database of accredited referees designed to end the use of forged, dishonest or unreliable references by past or current Oxfam staff.
The charity will not be issuing any references until this is in place.
Oxfam will also double the number of staff within its safeguarding processes and triple annual funding to more than $1m (£700,000).
Announcing the measures, Ms Byanyima said: "What happened in Haiti and afterwards is a stain on Oxfam that will shame us for years, and rightly so.
"In my language 'Okuruga ahamutima gwangye, mutusaasire'. It means 'From the bottom of my heart I am asking for forgiveness'."
On Thursday, Roland van Hauwermeiren, the former Belgian aid worker at the centre of the Oxfam sex scandal, broke his silence to deny allegations he used prostitutes or held sex parties while working for the charity.
On Friday, The Times reported a different aid worker sacked over the Haiti allegations was rehired two months later to work on another relief operation.
Crisis-hit Oxfam is facing a statutory inquiry by the Charity Commission while the Government has threatened to remove the charity's £31.7m annual funding.
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