Catering group Compass says an internal probe has found serious irregularities regarding work awarded to its Eurest Support Services (ESS) unit by the UN.
Compass is currently part of a wider United Nations probe
It found "issues in relation to the behaviour of a few individuals" at the service, but did not believe they extended beyond the individuals.
Compass, which has fired some ESS employees, is under investigation by US authorities over the contracts.
"This has been a highly regrettable episode for Compass Group," it said.
The senior management of Eurest Support Services has now been completely restructured, and new systems and controls have been put in place, including the reduction of the division's level of autonomy.
The UN suspended Compass in October after allegations of contract bidding irregularities.
It is alleged that ESS may have improperly obtained confidential information concerning a three-year contract to supply food and water to UN peacekeepers in Liberia.
In November, Compass sacked the head of its UK division and two other employees as the investigation continued.
The corruption allegations have also been referred to the UK's Serious Fraud Office.
Compass's own inquiry was led by Steve Lucas, the chairman of Compass Group's audit committee, and has lasted three months.
"We have now concluded a very thorough investigation and taken appropriate and decisive action," said Mr Lucas.
"We have no reason to believe the issues identified extend to any other part of the group.
"The board is determined Compass Group should meet the highest ethical and governance standards and is taking all necessary steps to ensure that this is the case."