Niger's government has accused the World Food Programme (WFP) of exaggerating fears the country could face another food crisis within months.
Niger's government says harvest has produced a food surplus
The WFP has asked for $19m (£11m) to avert shortages affecting 3m people.
But Niger's government - which denied there was mass starvation earlier this year - claims the recent harvest has in fact produced a food surplus.
Analysts say the impending crisis is the result of poverty, rather than the drought which affected crops in 2004.
This year the rains were good but because people used all their stocks to survive shortages before the harvest, they have little in reserve for the months ahead, the WFP says.
More than 1.2m of Niger's 12m population are thought to have sufficient cereal stocks only for the next three months, while a further 2m have stocks for five months at most.
Nearly 2m more face a precarious year struggling to maintain a bare livelihood, a WFP assessment found.
The BBC's Hilary Andersson in Niger says the government also has no stockpiles of food because all its reserves were used up this year.
Many people had to sell off their land to survive and now cannot produce enough food for the year ahead, she says, while others borrowed and are now in debt.
In the villages, most people are already living on a porridge of little nutritional value.
Although harvests this year were good, families' stocks are depleted
The feeding centres are filled with emaciated children and in some areas malnutrition rates are increasing, our correspondent adds, increasing the need for continued aid.
WFP spokesman Marcus Prior told the BBC: "If we don't get the money, there's a very strong risk that there are children here who will not receive the food that they need.
"We've already seen, in very graphic detail, exactly what that means. We cannot allow that to happen."
BBC Africa editor Martin Plaut says the impending shortages in Niger are a normal situation in one of the world's poorest countries, where many people live on the edge of hunger all the time.
Vast swathes of sub-Saharan Africa are similarly affected, he says, as population growth forces families to move into semi-desert areas that barely support farming.
Large families mean plots are then divided and sub-divided until they become so small they cannot provide food for everyone, he adds.