The apology comes as the Department of global development, which a year ago gave Oxfam more than £30 million, said it will review whether or not to continue to fund the charity.
Oxfam lied and failed in its "moral leadership" in the wake of allegations of sexual misconduct by aid workers, the International Development Secretary has said.
Speaking on BBC One's Andrew Marr Show this morning, Ms Mordaunt said she had only learned of the allegations against the charity when the Times reported them on Friday - and that she will hold urgent crunch talks with Oxfam's management tomorrow. Priti Patel, the former worldwide development secretary, revealed that more than 300 people in the wider aid sector had been accused of sexual abuse in the past year alone.
United Kingdom officials have said that Oxfam needs to hand over all its information on the issue in order to not lose funding.
Oxfam was further embroiled in scandal as reports claimed staff also used prostitutes in Chad during a humanitarian mission there in 2006.
"I have so much respect for Oxfam, they do great work, but this is a sector wide problem", the former staffer told the Observer.More news: Auto Expo 2018 highlights: Electric Vehicles steal the limelight
Mordaunt says there was a failure of "moral leadership" at Oxfam.
Oxfam said it was "shocked and dismayed" by the new Chad claims.
Ms Mordaunt announced she would meet the charity on Monday to discuss the case, and said: "If the moral leadership at the top of the organisation is not there then we can not have you as a partner".
A DfID spokesman said the way "appalling abuse of vulnerable people" had been dealt with raised serious questions for Oxfam. I made this our own agenda, I did my research, this [sexual abuse] is well-documented.
Speaking about the allegations, she said: "I think it's a complete betrayal of both the people Oxfam were there to help and also the people that sent them there to do that job".
"In the 21st century, it is utterly despicable that sexual exploitation and abuse continues to exist in the aid sector", she sad.More news: North Korea's Kim Invites S. Korean President for Summit: S. Korea
The charity added it will soon deliver a "safeguarding training course for faith organisations, especially churches, so they can understand, recognise and respond to safeguarding issues, and develop a safer culture".
There were fears Sunday that abuse allegations could spread to other aid charities.
Four members of Oxfam staff were dismissed and three, including the country director, resigned before the end of the 2011 investigation.
Penny Mordaunt said the charity had lied to the department at the time of the staff members' dismissal by telling them no aid beneficiaries were involved in the misconduct.
Oxfam has denied that they took part in any coverup thought according to reports they did not let the Haitian government what was happening which meant they were unable to take legal action against the employees involved.More news: Boston Herald Apologizes For Fake Story About Tom Brady
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