Financial Tribune- The risk of mass starvation in four countries-Nigeria, Somalia, South Sudan and Yemen-is rapidly rising due to drought and conflict, the UN refugee agency has warned.

About 20 million people live in hard-hit areas where harvests have failed and malnutrition rates are increasing, particularly among young children, the UNHCR said on Tuesday, Aljazeera reported.

In South Sudan alone-where the UN declared famine in some areas in February-"a further one million people are now on the brink of famine", Adrian Edwards, UNHCR spokesperson, said.

"We are raising our alarm level further by today warning that the risk of mass deaths from starvation among populations in the Horn of Africa, Yemen and Nigeria is growing."

A preventable humanitarian catastrophe, possibly worse than that of 2011 when 260,000 people died of famine in the Horn of Africa, half of them children, "is fast becoming an inevitability", he said.

"Overall, the UN has appealed for $4.4 billion for the four countries by the end of April, but has received less than $984 million or 21% to date," said Jens Laerke of the UN Office for Coordination of Humanitarian Affairs.