Aid agencies estimate some four million Somalis need food aid
The UN World Food Programme in Somalia has launched an inquiry into a report that thousands of sacks of aid were being sold on the open market.
Maize, wheat and cooking oil - marked not for re-sale and bearing the UN logo - were found in Mogadishu markets.
One trader told Britain's Channel 4 News he bought food from WFP staff who allowed them to load lorries freely.
Another trader said he invented fictional refugee camps, which were then allocated food that he sold.
"You go to the WFP office and fill in an application form to create a camp," he told Channel 4 News.
"When we receive the food, we give out some, and then divide the rest between ourselves and the WFP guys, who negotiated the deal."
The WFP denied that its staff were implicated but said powerful clans in war-torn Somalia may be involved.
Marcus Prior, a WFP spokesman for East Africa, said they were particularly concerned by the report of bogus refugee camps and had never before heard such an allegation.
"We take any allegation of food diversion extremely seriously and rigorously investigate all allegations that are drawn to our attention, as we are doing in this case," he told the BBC's Network Africa programme.
"And since we spoke to Channel 4, a separate unrelated investigation has also been launched."
The agency says it feeds at least 2.5 million people in Somalia every month - almost a third of the population.
It has had problems in the past ensuring its shipments even reach Somali ports, owing to a spate of attacks by gangs of pirates off the coast.