On Saturday the Charity Commission said that while Oxfam had reported that it was investigating inappropriate sexual behaviour, bullying, harassment and staff intimidation, it had not given the full details.
He said that it was very important to remember that "there are thousands of people working for Oxfam in some of the most hard places. and we must not forget that Oxfam is one of Britain's most brilliant charities".
Ms Mordaunt said the charity had also "categorically" stated to the Department for International Development (DfID) that no harm was done and beneficiaries were not involved.
Mordaunt called Oxfam's behavior "utterly despicable" and said the agency was suffering from a failure of "moral leadership".
In an emailed statement to dpa on Sunday, Oxfam said it would "strive to clarify as soon as possible whether the [Chad] allegations were known to us and what measures were taken".
The global development secretary has said the government will end funding to Oxfam unless the charity shows "moral leadership" and hands over all its information on its aid workers' apparent use of prostitutes in Haiti.
She challenged Oxfam bosses to explain why a resulting investigation saw four staff dismissed and three resign - with no public disclosure.
In its statement, Oxfam said it had informed its trustees, the government, as well as other major donors such as the European Union, the World Health Organization and other United Nations agencies of the investigation and the outcome. "We were not told about the nature of these events".
Oxfam condemned the behaviour of some former staff in Haiti.
Meanwhile, Oxfam is facing further allegations, reported in the Observer, that its staff used prostitutes in Chad in 2006. The charity had a fund worth more than $100 million to provide relief supplies and help rebuild Haiti's infrastructure, the Times reported.
Although the charity has denied covering up the alleged scandal, Christian Aid said the claims are "deplorable". While we can't corroborate the information at the moment it highlights again unacceptable behaviour by a small number of people and the need for a sector-wide approach to tackle the problem.
Ministers have launched an investigation into claims that foreign aid officials brushed off allegations of child abuse committed by aid workers.
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 cannot have you as a partner'.
Oxfam's chairwoman of United Kingdom trustees, Caroline Thomson, said it was working to "address the underlying cultural issues that allowed this behaviour to happen".
He added: 'Everybody - the 25,000 staff and volunteers - are compromised by this, the hundreds of thousands of people who support Oxfam every month are compromised by this, and to everybody I apologise. "What is so disturbing about Oxfam is that when this was reported to them, they completely failed to do the right thing", she said.