The cuts are "threatening to worsen already unacceptable levels of acute malnutrition, stunting and anemia, particularly in children," the UN's World Food Programme and refugee agency UNHCR said in a joint statement.
The heads of the two agencies were in Geneva Tuesday to make an urgent appeal to government representatives for more funds to help feed Africa's refugees.
"It is unacceptable in today's world of plenty for refugees to face chronic hunger," said UNHCR chief Antonio Guterres.
WFP will need $186 million by the end of the year to restore full rations and prevent cuts elsewhere, while UNHCR said it needed another $39 million to fund the nutritional support it provides to vulnerable refugees across the continent.
"Many refugees in Africa depend on WFP food to stay alive and are now suffering because of a shortage of funding," Ertharin Cousin said in a statement.
The funding crisis has forced WFP to cut rations for a third of the 2.4 million refugees it helps feed in 22 African countries, with more than half of the 800,000 affected refugees seeing rations slashed by at least 50 percent.
The situation was most dire for the 300,000 refugees in Chad -- mainly from Sudan's Darfur region and from the Central African Republic -- whose rations had been cut by as much as 60 percent, the statement said.
Refugees there were in many cases left with rations of just 850 calories per day, compared to the recommended 2,100 calories adults should receive to remain healthy.
The situation was not much better for some 150,000 refugees in Central Africa or in South Sudan, where supplies had also been cut by at least 50 percent, while another 338,000 refugees in Liberia, Burkina Faso, Mozambique, Ghana, Mauritania and Uganda had seen their rations dwindle up to 43 percent, the UN agencies said.
