Food rations to more than one million Eritreans are being cut because of a slow response by donors to aid appeals.
Eritreans have become dependent on food handouts
The World Food Programme says it has just 70,000 tonnes of food left in its warehouses and no more supplies will arrive until June.
Four years of drought have hit Eritrea and nearly half of its four million people are chronically malnourished.
Neighbouring Ethiopia has had a bumper harvest, but Eritrea cannot import food because the border was shut by a war.
Since the 1998-2000 conflict, there have been successive droughts. Food prices have risen and water is being sent into some districts.
In January, the UN warned that some two-thirds of the population of Eritrea would require varying degrees of food assistance this year.
The head of the WFP in Eritrea, Jean Pierre Cebron, says it will be a close-run thing to ensure current stocks last until the arrival of new food aid.
"We will have to do our best to accelerate the transportation and distribution. We have to try. It is our job. But I am worried."