"We must learn from what happened in Niger and not let the situation deteriorate," World Food Programme (WFP) spokeswoman Christiane Berthiaume said on Friday.
"We're appealing to donors to act now and not to wait as long as they did with Niger - because it is deteriorating."
Officials are reworking plans to supply food to 1.2 million people threatened with famine in Mali, Berthiaume said.
Last week, the United Nations warned that food shortages were bearing down on millions of people in Niger, Mali, Mauritania and Burkina Faso due to the same locust- and drought-induced famine and increased its emergency funding appeal five-fold to $81 million.
The new plan for Mali would take that budget over the $81 million mark, Berthiaume said.
The WFP also said cash shortages and logistical breakdowns are hampering efforts to feed millions in southern Sudan at the height of Africa's "hunger gap" and rainy season.
In southern Sudan, a myriad of complications had delayed attempts to transport rations.
Thousands of displaced persons are returning to the area after a historic peace deal signed in January ended Africa's longest-running rebellion.
In Sudan, complications have
delayed bid to transport rations
"WFP's response is severely hampered by critical funding shortages ... as well as limitations on road deliveries and airlifts imposed by the rainy season," an agency statement said.
Forced to borrow
"These problems sabotaged WFP's efforts to deliver by air and pre-position food aid before rains cut road access in much of the south," it said.
The WFP has been forced to borrow funding from within the agency to make up a $137 million shortfall - 45% of its 2005 budget - to feed 3.2 million people in southern Sudan.
"Contributions are urgently needed," the agency said.
The lack of storage for jet fuel for food drops has also hampered relief efforts, WFP said.
In a search for alternatives, the agency has repaired 600km of roads in difficult areas so that its trucks could pass, and has attempted to use barges on the Nile.