JOHANNESBURG -- The United States on Saturday announced more than US$630 million in aid for Yemen, Somalia, South Sudan and Nigeria, where conflict has helped to cause what the United Nations calls the world's largest humanitarian crisis in more than 70 years.

The announcement came as President Donald Trump attended the Group of 20 summit in Germany. "This is truly a life-saving gift," said David Beasley, the new American director of the U.N.'s World Food Program.

While the United States is the world's largest humanitarian donor, Trump's proposed deep cuts to foreign aid -- more than 30 per cent -- have caused widespread concern.

"We welcome President Trump's attention to the global humanitarian crisis, but he was announcing aid that Congress approved months ago and that his administration has delayed," Rev. David Beckmann, president of the Washington-based Christian organization Bread for the World, said in a statement.

The total U.S. humanitarian assistance to the four countries is now more than $1.8 billion this fiscal year, the U.S. Agency for International Development said.

Tens of millions of people in Yemen, Somalia, South Sudan and Nigeria face hunger amid conflict. Yemen has the world's largest cholera outbreak, while half of drought-hit Somalia's 12 million people need aid. South Sudan's civil war and Nigeria's Boko Haram insurgency have contributed to severe hunger.

The WFP said in a tweet that the new U.S. donation "comes just as families face the time of year when food stocks run out." The U.N. agency earlier this year warned that food aid could be cut for more than a million hungry Nigerians if promised funding from the international community didn't arrive.

In May, Trump announced $329 million in "anti-famine" aid to the four countries.

While the Trump administration's 2018 spending plan does not eliminate money for emergency food aid, it ends a critical program by consolidating it into a broader account that covers all international disaster assistance. Doing so reduces the amount of money the U.S. dedicates to fighting famine to $1.5 billion next year, from $2.6 billion in 2016.

Trump officials say the proposed changes will streamline U.S. aid programs, eliminate redundancies and increase efficiency. Relief organizations fear less U.S. money will mean an increase in famine and hunger-related deaths, particularly in Africa, if Congress approves the budget.