Oxfam should have been more open about allegations of sexual abuse by its workers in Haiti, its chief executive has said.
Mark Goldring said the charity needed to "win back the trust" of the British people after it was rocked by accusations it had covered up claims that staff used prostitutes while delivering aid.
His apology in a column in the Sunday Mirror was of a different tone to the one struck on Friday, when Mr Goldring told the Guardian critics were "gunning" for his organisation and suggested no-one had "murdered babies in their cots".
Meanwhile, the Charity Commission said it had already seen "increased reporting" from the sector following the Oxfam revelations - as it announced a new taskforce to look at safeguarding incidents.
Mr Goldring will be hauled before MPs to answer questions about Oxfam's aid work on the Caribbean island, parts of which were devastated by an earthquake in 2011.
He wrote: "We are sorry for the mistakes we have made. We should have been more open with the public about the fact that staff in Haiti were fired for sexual abuse. And we should have expanded our safeguarding team faster."
He added: "As an organisation that fights for women's rights, the abuse of women in Oxfam's name is particularly hard to bear."
The head of Oxfam International described the damning sexual exploitation allegations its faces as a "stain" on the charity "that will shame us for years" as she announced plans to try to stamp out abuse in the organisation.
Executive director Winnie Byanyima promised to root out any wrongdoing at the charity and provide justice for anyone abused by its staff.
Mr Goldring echoed this, writing: "We know we need to learn and change. And we will listen every step of the way.
"We have made big improvements since 2011 including setting up a confidential whistleblowing hotline but we know this is not enough. This week we have begun a plan of action to make sure we do everything we can to ensure that sexual exploitation doesn't happen under our watch.
"It is the generosity of the British people that has enabled us to grow and reach more and more people. We must win back their trust so that we can continue to deliver Oxfam's work which helped 11.6 million people last year."
The Charity Commission said its new taskforce would ensure any gaps in serious incident reports across the sector were filled and that it would "intervene in serious cases where the Commission is concerned that trustees are not fulfilling their legal duties".
Chief executive Helen Stephenson said: "I want to be 100% certain that we have done everything in our power to ensure reports we received, including those which we have cause to believe may be incomplete or inadequate, were properly handled, ensure follow up and to give regulatory advice to charities on the right actions to take.
"The team's work will reassure us, and the public, that charities have and are being transparent and open with the regulator, and that we are holding charities properly to account.
"It goes without saying that we will deal swiftly and robustly with concerns that this work discovers."