United Nations (CNN) -- The United Nations remained abuzz Wednesday as Secretary-General Ban Ki-moon returned to New York headquarters days after an internal report from a senior staffer sharply chastised him.
Ban, fresh from a trip to Afghanistan, met with British Prime Minister David Cameron Wednesday afternoon. But those discussions have taken a back seat to the controversy surrounding a leaked 50-page memo from the outgoing U.N. anti-corruption director.
Swedish diplomat Inga-Britt Ahlenius wrote in the memo that the U.N. is "drifting into irrelevance" under Ban's supervision.
Ahlenius wrote that the U.N. seems "to be seen less and less as a relevant partner in the resolution of world problems," saying Ban has led his office into a "process of decay."
One Western diplomat voiced concern Wednesday that Ahlenius' personal attacks against Ban undermine her case, saying that Ban has in fact shown good leadership in some areas. But if there are systemic problems within the U.N., said the diplomat, they should be pointed out and addressed.
The secretary-general's spokesperson, Martin Nesirky, echoed this Wednesday. He said that his office is "looking seriously at the constructive, substantive elements within that end-of-assignment report."
"It's really important to understand that constructive criticism is welcome and necessary to help to move forward a large organization like this," Nesirky said.
However, he was quick to stress the office would correct any "inaccuracies or misrepresentations" raised in Ahlenius' letter.
Ahlenius left her post as the head of the department charged with combating U.N. corruption in mid-July after serving out her five-year term. As her tenure at the Office of Internal Oversight Services came to an end, she sent a shockwave throughout the U.N. with an "end-of-term" report to her boss admonishing the secretary-general for his "absence of strategic guidance and leadership."
The report was leaked to the Washington Post, which has posted a three-page summation from Ahlenius on its website along with a responding letter from Vijay Nambiar, Ban's chief of staff.
The OIOS had no comment Wednesday following the revelations contained in their former administrator's memo.
Swedish Foreign Minister Carl Bildt told reporters at a press briefing in Stockholm Wednesday that he had not read Ahlenius' report, but "traditionally there is a tension between Ahlenius' unit and the (office of the secretary-general)," calling the friction "only natural" as reforms are sought within the U.N.
Although such disapproval from a U.N. insider is uncommon, Ahlenius' report is not the first time Ban has faced brash condemnation.
In August 2009, a confidential memo from Norwegian Deputy Ambassador Mona Juul to her foreign minister was leaked. Juul referred to the secretary-general as "spineless and charmless," saying that Ban was "struggling to show leadership" with "irresolute" appeals and that he was "lacking in dedication."
Michael Soussan, a former U.N. staff member who helped blow the whistle on the oil-for-food scandal, once briefed Ahlenius as part of her understanding of the U.N. He told CNN that her statements are "courageous," saying it was time "for someone to give voice this."
Soussan believes many staffers feel there is a "lack of proper management" currently at the U.N. and Ahlenius' memo "is welcome."
"She has done the U.N. a favor," he says. "There is a culture of secrecy, which ultimately harms the organization."
Nambiar opposes this viewpoint, writing in his responding letter to Ahlenius that "transparency and accountability would be the cornerstone" of Ban's tenure.
He has had to strike a balance between running the United Nations and "providing truly global leadership," Nambiar writes of the secretary-general. He calls a number of Ban's efforts "visionary," including on climate change and women's empowerment, writing that the secretary-general has "led from the front on important political issues from Gaza to Haiti to Sudan."
Ahlenius disagrees, questioning if his leadership has led to any improvement in the institution's "capacity to protect civilians in conflict and distress? What relevance do we have in disarmament, in Myanmar, Darfur, Afghanistan, Cyprus, G20...?"
But the Western diplomat calls these critiques "unfounded" because Ahlenius was never directly involved in policy issues.
Peter Yeo, executive director of the Better World Campaign, an organization dedicated to fostering a productive relationship between the United States and the United Nations, cited a series of transparency and accountability initiatives implemented under Ban as "real progress toward reform."
However, Ahlenius fundamentally disputes this claim. "There is no transparency, there is lack of accountability," she writes. "I do not see any signs of reform in the organization."
Yeo urges moving forward and quickly finding a new OIOS chief, writing that "it would be unhelpful to allow this back-and-forth to become a distraction to reform efforts at the U.N."
Spokesperson Nesirky said Wednesday that a replacement will be named very soon.
But according to Ahlenius, Ban's mismanagement from the top "translates into a weakening of the overall position of the United Nations," and wonders whether the U.N. is on the right path under Ban's supervision.
"This is as sad as it is serious," she writes.
CNN's Per Nyberg and Senior U.N. Correspondent Richard Roth contributed to this report.