Cuts in food rations for 1.5 million refugees in east Africa, due to funding shortages, could increase school dropouts, crime and malnutrition, a United Nations official said on Wednesday.

With humanitarian needs soaring around the world, donors are prioritising crises in Syria, Yemen and Bangladesh, said Peter Smerdon, the World Food Programme (WFP)'s east Africa spokesman.

As a result, refugees in Kenya, Ethiopia, Tanzania and Rwanda fleeing drought and conflict have had maize, beans and vegetable oil rations cut by almost a third over the last seven months, he said.

"In my 15 years at WFP, I have never seen this number of refugees, at this time of year, having cuts to their food rations," he said.

"Needs have gone through the roof for the whole of the humanitarian system, and donors really can't keep up with these increased needs. And the longer they continue, the more likely people will fall through the cracks."

The four east African nations provide sanctuary for millions fleeing drought in the Horn of Africa and protracted conflict in Somalia and South Sudan - the world's youngest nation - where civil war has created the continent's biggest refugee crisis.

WFP has only received about one-fifth of almost $360 million required to support refugees in Ethiopia, Kenya, Rwanda and Tanzania in 2018, Smerdon said.

He warned that WFP would have to further reduce rations if funding did not come through.

"If you a cut a refugee family's rations, they will take their kids out of school to save money on costs such as uniforms and books, and send them out to either find food or work," he said.

"In a refugee camp, crime is likely to go up as people are likely to go into debt as people are already pretty poor. Over the longer term, child malnutrition will go up."