The UN World Food Programme has expressed concern that it has received less than 20% of the funds it asked for to help flood victims in Bangladesh.
Bangladesh suffered from its worst flooding in six years
The WFP had appealed last month for $74m from donor countries.
But a WFP representative in Dhaka told the BBC there had been a very poor response to the request.
More than 600 people died in the floods, which destroyed rice crops leaving 20 million people likely to be dependent on food aid for months.
The WFP says it wants to provide food aid to flood victims in return for repairing roads, dykes and embankments in a long-term strategy that would help protect them from the next disaster.
Douglas Casson Coutts, the WFP representative in Dhaka, says many donor countries assumed that the receding waters meant the problem was over.
"It's frustrating, I think, that we obviously have had difficulties to get the world community to focus specifically on the situation here," he told the BBC.
The WFP says that with the flood victims leaving the emergency shelters, they need assistance not only to restore their households but also to acquire skills and assets that will arm them against the next disaster.
But without more funds coming in, it will be force to curtail its plans.
"If we don't have enough money, we will do what we can with our limited funds we have available so far.
"But it will be much less than we had originally planned for," Mr Coutts said.
The Bangladeshi minister of food and disaster management, Chowdhury Kamal Ibne Yusuf, told the BBC that there was sufficient financial support to fulfil the government's promise to feed five million families.
Last month, the UN urged the international community to offer more aid to help the flood victims in Bangladesh.