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 today 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.
"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.
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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 per cent.
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 per cent, while another 338,000 refugees in Liberia, Burkina Faso, Mozambique, Ghana, Mauritania and Uganda had seen their rations dwindle up to 43 per cent, the UN agencies said.
"The number of crises around the world is far outpacing the level of funding for humanitarian operations, and vulnerable refugees in critical operations are falling through the cracks," said Guterres.
He warned that even small cuts to rations could spell disaster for already undernourished people, with the impact, especially on children, "immediate and often irreversible".
Refugees hit by ration cuts were desperately looking for ways to put food on the table, with the crisis pushing more and more children to quit school to seek work and prompting families to marry off their girls at a younger age.