Stephen O'Brien told the UN Security Council that "without collective and coordinated global efforts, people will simply starve to death" and "many more will suffer and die from disease," RFE/RL wrote.

He urged an injection of $4.4 billion in emergency aid by July for Yemen, South Sudan, Somalia, and northeast Nigeria, plus safe and unimpeded access for humanitarian aid "to avert a catastrophe."

Read alsoPortugal recognizes Ukraine Holodomor in 1932-1933 as genocideWithout a major infusion of money, he said, children will be stunted by severe malnutrition and won't be able to go to school, gains in economic development will be reversed and "livelihoods, futures and hope will be lost."

The UN defines famine as when more than 30 percent of children under age 5 suffer from acute malnutrition and mortality rates top two per 10,000 people every day.

"We are facing the largest humanitarian crisis since the creation of the United Nations," O'Brien said, with the worst crisis in Yemen, where two-thirds of the population needs aid and more than seven million people are hungry.