The United Nations' internal investigations office has uncovered serious lapses and due-diligence failures in the world body's interaction with organizations tied to an alleged bribery scheme involving a former U.N. General Assembly president.

The 21-page confidential report by the U.N. Office of Internal Oversight Services (OIOS), reviewed by Reuters, outlines the results of an audit ordered by Secretary-General Ban Ki-moon in response to charges against John Ashe, General Assembly president in 2013-2014, and six other people.

The report gave the U.N. an overall grade of "partially satisfactory" in the March 22 report, which is available to U.N. member states on request. It noted "important deficiencies" in the way United Nations and its staff interacted with nongovernmental organizations (NGOs) and oversees U.N. employees.

It is the biggest financial corruption crisis to rock the United Nations since the oil-for-food scandal hit the world body during the tenure of Ban's predecessor, Kofi Annan. U.N. officials and diplomats say the latest scandal highlights the need for greater transparency at the United Nations.

OIOS recommended improvements in internal U.N. risk management and controls in light of the irregularities uncovered -- a U.N. document improperly altered, travel expenses paid by NGOs against U.N. guidelines, U.N. employees keeping iPads given to them by an NGO headed by an indicted individual.

OIOS urged Ban to ensure that any outside organizations the U.N. deals with are properly vetted. It also said the U.N. should review any continuing relations with NGOs linked to the indictment. 

The audit came in response to an ongoing U.S. investigation that has since October resulted in charges against seven people including Ashe, a former U.N. ambassador from Antigua and Barbuda.

U.S. prosecutors say Ashe received $1.3 million in bribes from Chinese businessmen including Ng Lap Seng, a billionaire real estate developer who heads Macau-based Sun Kian Ip Group and was seeking to build a U.N.-sponsored conference center in Macau.

Francis Lorenzo, a suspended deputy U.N. ambassador from the Dominican Republic who prosecutors said helped facilitate Ng's bribes and received bribes himself, pleaded guilty in March and agreed to cooperate with U.S. authorities. Sheri Yan, chief executive of Global Sustainability Foundation, a New York-based NGO, and Heidi Hong Piao, its finance director, accused of facilitating bribes to Ashe, pleaded guilty in January. Julia Vivi Wang has not yet entered a plea, and Ng's assistant Jeff Yin pleaded not guilty. 

Attorneys for those charged either did not respond or declined to comment when contacted by Reuters. A spokesman for the Manhattan U.S. attorney's office also declined to comment.

U.N. spokesman Stéphane Dujarric said that while the secretary-general was glad that the audit found many controls working properly, the flagged procedural lapses were a concern.

"Instructions reinforcing the correct procedures with respect to document issuance have been issued to the Departments and Offices concerned," Dujarric said. 

"With regard to the specific cases referred to in the audit, action is being taken to determine responsibility and any measures, including possible disciplinary action, that may be deemed appropriate," he said, adding that the U.N. was committed to cooperating with the U.S. authorities.

The most serious lapse OIOS identified involved a Feb. 24, 2012 letter from Ashe to Ban supporting the Macau center that was "reissued for technical reasons" on June 6, 2013.

OIOS said the amended letter, which U.S. prosecutors say was crucial in aiding Ng's plans for the Macau center, should have been cleared with Ban's office first and then flagged as a "revision," not a reissue. 

The revisions included mentions of Ng's group as the representative for the center's implementation and South-South News, founded by Ng, as the project's "leading partner." 

Lorenzo was president and Wang vice president of South-South News, which remains among media organizations accredited to the U.N. South-South News did not respond to a request for comment.

OIOS said commercial enterprises should never be mentioned in official U.N. documents, unless they qualify for an exception, which was not the case here.

The audit said the irregularities "assume significance" in the context of the allegations against Ashe and the role the document played in the alleged scheme. "It is therefore essential that responsibility is assigned for these lapses, and steps are taken to prevent possible misuse of authority in publishing official documents of the United Nations," it added. 

It was not immediately clear if assigning responsibility for reissuing the document could lead to further charges. U.S. authorities say at least two unnamed U.N. employees were involved in amending the document.

The report also cited an August 2015 conference in Macau, co-sponsored by Sun Kian and the U.N. Development Program (UNDP), whose participants, among them several U.N. staff members, received iPads worth $599 plus tax from the organizers.

Three U.N. staffers told OIOS they handed over the devices to their superiors immediately upon return from Macau, while four others did not do so until later.

The audit recommended that the U.N. Ethics Office issue more specific guidance on gifts to avoid conflicts of interest.

The UNDP is an autonomous U.N. agency and is conducting its own audit, due to be released soon. Last week the U.N. released a report recommending new ethical rules and financial disclosures for the General Assembly president's office.