"Your actions are not only deplorable, but seriously reprehensible . . . . Your action is without precedent and in my opinion seriously embarrassing for yourself," she wrote in the memo after her five-year term presiding over the Office of Internal Oversight ended.
After the UN's oil-for-food program in Iraq was revealed to be frought with corruption, Ban took over as secretary-general in 2007. He hoped to cleanse the agency's reputation.
Swedish Foreign Minister, Carl Bildt, says he hasn't read Ahlenius' letter, but adds that much of the blame in the slow pace of reforms within the UN should be placed with the General Assembly, which maintains old structures because they suit different countries' interests.