Updated

Secretary-General Antonio Guterres says the United Nations needs $4.4 billion by the end of next month to prevent "a catastrophe" of hunger and famine in South Sudan, Nigeria, Somalia and Yemen. Just $90 million has been collected so far.

Guterres said Wednesday that over 20 million people altogether are going hungry in those countries. Amplifying concerns that other U.N. officials expressed recently, Guterres said the world "is facing a tragedy" and "must avoid it becoming a catastrophe."

Children's agency UNICEF warned Tuesday that almost 1.4 million children are at "imminent risk of death" from acute malnutrition this year in the four countries. Already, famine was declared Monday in parts of South Sudan's Unity state.

Guterres says he believes governments and other donors will step up financially to help.