US President Donald Trump promised $639 million in aid to feed people facing starvation because of drought and conflict in North-eastern part of Nigeria, Somalia, South Sudan and Yemen.

Of the funding, $121 million would go to Nigeria, according to Rob Jenkins, Acting Head, Bureau of Democracy, Conflict and Humanitarian Assistance at the US Agency for International Development (USAID).

Similarly, more than $191 million would go to Yemen, $199 million to South Sudan and nearly $126 million for Somalia.

"With this new assistance, the US is providing additional emergency food and nutrition assistance, life-saving medical care, improved sanitation, emergency shelter and protection for those who have been affected by conflict," USAID said in a statement

Jenkins, according to the News Agency of Nigeria (NAN), said conflicts in all the four countries had made it difficult to reach some communities in need of food.

"We're in a dire situation right now. The situation in southern Ethiopia fortunately does not rise to the dire situation of the other four, but the situation is deteriorating and might very well be catastrophic without additional interventions," he said.

Jenkins said USAID was also concerned about the situation in southern Ethiopia, adding that Washington had already provided some $252 million this year to Ethiopia, "but the needs continue to grow."

President Trump's pledge came during a working session of the G20 summit of world leaders in Hamburg, Germany, the UN World Food Programme (WFP), Executive Director, David Beasley, said on the sidelines of the meeting, according to Reuters.

"We're facing the worst humanitarian crisis since World War Two," Beasley said, describing the pledge as providing a "godsend" to the suffering millions and the global food agency fighting hunger worldwide.

The new funding brings to over $1.8 billion aid promised by the US for fiscal year 2017 for the crises in the four countries, where the UN had estimated more than 30 million people needed urgent food assistance.

Beasley said the US funding was about a third of what the WFP estimated was required this year to deal with urgent food needs in the four countries in crisis as well as in other areas.

The WFP estimates that 109 million people around the world will need food assistance this year, up from 80 million last year, with 10 of the 13 worst-affected zones stemming from wars and "man-made" crises, Beasley said.

"We estimated that if we didn't receive the funding we needed immediately that 400,000 to 600,000 children would be dying in the next four months," he said.

Trump's announcement came after his administration proposed sharp cuts in funding for the US State Department and other humanitarian missions as part of his "America First" policy.

Beasley said the agency had worked hard with the White House and the US government to secure the funding, but Trump would insist that other countries contributed more as well.