"There is nothing more outrageous and dishonest than a sexual predator who uses his position as part of the humanitarian response to a natural disaster to exploit needy people in their moment of greatest vulnerability," he tweeted.
Several former members of Oxfam's local staff had said they tried to raise concerns but felt their complaints were ignored, the BBC reported.
One of the UK's biggest charities, Oxfam was the subject of a report in the Times newspaper last week. The article accused the charity of concealing the findings of a 2011 inquiry into claims that senior aid workers, including Haiti's National Director, paid local prostitutes for sex.
Oxfam was in the country offering relief following a devastating 7 magnitude earthquake that killed over 200,000 people in 2010.
The charity has since confirmed that sexual misconduct occurred and that several staff members were dismissed or resigned after the internal investigation, but denies any cover-up.
It has been accused by a British charity watchdog, which launched an inquiry, of failing to disclose the full details.
Pierre Esperance, the head of Haiti's National Human Rights Defence Network, said: "Oxfam, after the earthquake, became like a factory."
"A big organisation with a lot of people with bad management. People who don't have any skill regarding development, with a lot of money, and this is the result."
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)