Fleurant is in charge of the oversight of aid agencies.
"They have been poorly served by Oxfam's leadership team too".
Several children said they knew of cases where worldwide aid workers had left the country while wanted by police, or where abusers had been disciplined or assigned to a different post.
The charity said it had received a reference from someone claiming to be his former Oxfam boss, sent from a private email account.
Addressing the allegations, Van Hauwermeiren acknowledged his behavior was unacceptable.
"I am not ideal, I am not a saint - a man of flesh and blood and have made mistakes (not easy to admit), and I am deeply ashamed", he wrote.
The comments from Haitian President Jovenel Moise add to the condemnation the anti-poverty charity has received since the Times of London revealed last week some Oxfam employees paid for sex while working in Haiti among people devastated by the 2010 quake.
U.K. International Development Secretary Penny Mordaunt has warned that British government funding to the group - some 31.7 million pounds ($43.8 million) in 2016-17 - is at risk unless it comes clean about the allegations.
The head of the British wing of Oxfam claims that his charity is being unduly criticised over the sex scandal and claims the episode is being used to attack the global aid industry. The agency also offers assistance to people after emergencies and disasters.
Ms Byanyima said Oxfam was "very hurt" but insisted the charity would survive the scandal. "Oxfam has now confirmed that they have complied with all of these points".
Also Tuesday, Britain's charity watchdog opened an inquiry into how Oxfam handled the allegations of sexual abuse in Haiti in 2011.
Oxfam relies on public and corporate donations as well as government funding. I'm here for all the women who have been abused.
An "urgent and independent" review of Oxfam's culture and practices has been announced, and will be lead by prominent women's rights experts.
Ms Mordaunt said she had made three demands of Oxfam - that it makes clear how it will handle any future allegations, that staff members involved are reported to their national governments and that it cooperates with the Haitian authorities.
"Oxfam will be a standard bearer of safety and dignity for all who interact with us", she said on twitter.
Asked how old she was when she started having sex with him she said: 'Seventeen, because it was right after I had the child.' The age of consent in Haiti is 18. I am inviting anyone who has been a victim of abuse to come forward. "Not to be afraid", Guterres told CNN Friday.
"Our own fieldwork suggests that the scale of abuse is significant", the report concluded.
On Wednesday, Doctors Without Borders, which sends medical staff around the world to regions stricken with war and disease, said it had dealt with 24 cases of sexual harassment or abuse among its 40,000 staff previous year, and dismissed 19 people as a result.
Since the revelations were first reported in The Times last week, Oxfam has lost two high-profile ambassadors, the actor Minnie Driver and Nobel Peace Prize victor Archbishop Desmond Tutu.