The United Nations (UN) agencies for food and refugees plan deep cuts due to an unprecedented plunge in funding, including from former top donor the US, internal memos sent to staff show, raising questions about how to maintain hunger relief.

The humanitarian sector has been roiled by funding cuts from major donors, led by the United States under President Donald Trump, and other Western countries as they prioritise defence spending prompted by growing fears of Russia and China.

The World Food Programme (WFP), a Rome-based UN agency, warned last month that 58-million people are at risk of extreme hunger or starvation unless urgent funding for food aid arrives. Millions of people facing acute food shortages in Sudan could be affected, the WFP said on Friday.

In an internal memo sent to staff on Thursday and seen by Reuters, WFP director Stephen Omollo said that the cuts were necessary due to the "unprecedented funding environment", with the 2025 donor outlook at $6.4-billion, or a 40% reduction versus last year. He did not name any countries responsible.

"We remain concerned that the situation shows no sign of improving," he said, adding that the planned cuts might not be sufficient and that further downsizing was being explored.

"In this challenging donor environment, WFP will prioritise its limited resources on vital programmes that bring urgently needed food assistance to the 343-million people struggling with hunger, and increasingly facing starvation," the WFP said in a statement to Reuters.

The United States, Germany, Britain and the European Commission have been among the top donors in recent years, its website showed. WFP, like many United Nations agencies, relies entirely on voluntary donations.

The note to staff from UN High Commissioner for Refugees (UNHCR) chief Filippo Grandi dated April 23 said that it planned an overall reduction in costs of 30% and that the number of senior positions would be cut in half.

"We will have to close some country offices, instead covering these countries through strengthened multi-country office structures," Grandi said.

UNHCR spokesperson William Spindler told a Geneva press briefing that the agency has been severely affected by funding uncertainty. "We have had to respond to this by stopping a lot of work we have been doing in the field," he said.

A second spokesperson later added that UNHCR was undertaking a comprehensive review of its operations, staffing and structures, declining to give a timeline since the review is ongoing.