The World Food Programme has demanded Yemen’s rebel Houthi movement stops diverting desperately needed food aid from people in areas under its control.
A survey by the UN agency said people in the capital Sanaa had not received rations to which they were entitled.
The WFP said lorries were illegally removing food from distribution areas, with rations sold on the open market or given to those not entitled to it.
There was no response from the Houthis, but they have denied diverting aid.
The UN says some 20 million Yemenis are food insecure and that 10 million of them do not know how they will obtain their next meal.
Yemen has been devastated by a conflict that escalated in 2015, when a Saudi-led coalition intervened after the Houthis seized control of much of the west of the country and forced President Abdrabbuh Mansour Hadi to flee abroad.
At least 6,800 civilians have been killed and 10,700 injured in the fighting, according to the UN. Thousands more civilians have died from preventable causes, including malnutrition, disease and poor health.
The WFP said the misappropriation of aid came to light in a review conducted in recent months, prompted by an increasing number of reports of humanitarian food for sale on the open market in Sanaa.-BBC