UNITED NATIONS -- 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.”

“The situation is dire,” Guterres said in a joint press conference Wednesday at the United Nations. “Millions of people are barely surviving in the space between malnutrition and death, vulnerable to diseases nd outbreaks, forced to kill their animals for food and eat the grain they saved for next year’s seeds.”

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.

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

“The lives of millions of people depend on our collective ability to act,” Guterres said. “In our world of plenty, there is no excuse for inaction or indifference. We have heard the alerts. Now there is no time to lose.”