The UK's Department for International Development sharply criticised the charity for its lack of transparency as questions swirled about how much detail Oxfam provided when it first reported the allegations.
The agency, which gave 31.7 million pounds (USD 43.8 million) to Oxfam last year, demanded that Oxfam's senior officials meet with it to explain their actions.
"If wrongdoing, abuse, fraud or criminal activity occur, we need to know about it immediately, in full," the agency said.
It said Oxfam's investigation into the charges was hampered by a "determination to keep it out of the public eye."
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Oxfam says it investigated the allegations in 2011. The charity confirmed it had dismissed four people and allowed three others to resign in the case after an investigation uncovered offenses including sexual misconduct, bullying, intimidation and failure to protect staff.
The charity commission demanded further information from Oxfam on Saturday, saying it had "made no mention of any potential sexual crimes involving minors,' when it first reported the investigation in 2011.
"Our approach to this matter would have been different had the full details that have been reported been disclosed to us," the commission said.
Oxfam said yesterday the behaviour in Haiti was "totally unacceptable, contrary to our values and the high standards we expect of our staff." On Saturday, Oxfam was forced to deny further reports that it gave positive references to those it dismissed.
Oxfam said some former workers may have falsified references or asked individual staff members to provide references, but said it couldn't prevent such actions.