The Niger government has said it would be "foolish" to distribute free food, as demanded by some 2,000 protesters on Thursday in the capital, Niamey.
Some children have died from starvation
More than 3.5m people need food aid after poor rains and a locust invasion, and some accuse the government of ignoring the crisis.
But a government spokesman Mohamed Ben Omar said that its food stocks could not be handed out for free.
The UN says it has not had a single pledge for money for its Niger appeal.
The UN Office for the Coordination of Humanitarian Affairs has called for $16.2m to buy food for those suffering from recurring drought and a locust infestation.
Some 150,000 young children are said to be severely malnourished already.
"What civil society is asking is poorly conceived and irrational. The state of Niger cannot engage in such a foolish adventure," Mr Omar told the AFP news agency.
He said Niger's emergency food stocks had been built up carefully and would need to be replaced if they were given out.
On Thursday, some 2,000 people marched through the capital, Niamey, demanding immediate food aid.
One of the rally's organisers, Amadou Bello, said rice and millet was needed now because international aid would take too long to arrive.
"We are hungry" and "Give us food", they shouted in front of parliament.
The organisers of the march, the Democratic Co-ordination of Niger Civil Society (CDSN), accuse the government of not doing enough to prepare for the "hungry season" which was bound to follow a poor rainy season last year.
The rainy season finished last October and it was obvious that supplies would not last through until the next harvest, they say.
Some children have already starved to death.