Thousands of displaced Somalis rely on food aid from WFP
The UN World Food Programme has denied a claim that up to half the food aid to Somalia was being diverted to Islamist militants and corrupt contractors.
WFP officials said there was no evidence to back up the claim made in a report by a UN monitoring group.
The UN's aid chief in Somalia said the report was based on "hearsay" and not backed up by any documentary evidence.
The aid chief, Mark Bowden, said the flow of funds to the WFP operation in Somalia had dropped after the report.
The UN Monitoring Group on Somalia was initially set up by the Security Council to supervise the arms embargo against the war-torn country.
Their critical report was leaked to the news media earlier this month.
It said food aid was diverted to a web of distributors, transporters and armed groups, with some local UN workers also taking a cut in the profits.
It blamed the problem on the food distribution system in the war-torn country, where transporters have to navigate roadblocks manned by various militias and bandits.
The "estimates of diversion are not apparently based on any documentation but rather on hearsay and commonly held perceptions," Mr Bowden wrote in a letter dated 23 March quoted by news agencies.
"They do not provide the evidential basis for discussion that was the hallmark of previous Somalia Monitoring Group reports," he said.
The head of the WFP, Josette Sheeran, said in Geneva on Thursday that there were "no facts to support" the monitoring group's report.
She said Somalia was "certainly the most dangerous and complex operation we face".
Charges that food aid was being diverted first surfaced in 2009. The US has since reduced funding to Somalia, fearing that aid was falling into the hands of the hardline Islamist group al-Shabab.
The World Food Programme has also struggled to keep up with food deliveries.
Last month, al-Shabab banned the food agency from operating in Somalia.
The WFP said it had already announced a suspension of its work in the southern part of the country because of attacks and extortion by local militants.