The United Nations appealed Friday for Sudan's battling factions to allow delivery of humanitarian relief to fend off looming "catastrophic" hunger.

Some five million Sudanese could face calamitous food insecurity in coming months as a nearly yearlong war between rival generals continues to tear the country apart, according to a UN document seen Friday by AFP.

The war between army chief Abdel Fattah al-Burhan and his former deputy, Mohamed Hamdan Daglo, has since April last year killed tens of thousands, destroyed infrastructure and crippled the economy.

It has also triggered a dire humanitarian crisis and acute food shortages, with the country teetering on the brink of famine.

Noting that some 18 million Sudanese are already facing acute food insecurity -- a record during harvest season -- UN humanitarian chief Martin Griffiths warned in a letter to the Security Council that "almost 5 million people could slip into catastrophic food insecurity in some parts of the country in the coming months."

He noted that nearly 730,000 Sudanese children -- including more than 240,000 in Darfur -- are thought to suffer from "severe" malnutrition.

"Aid organizations require safe, rapid, sustained and unimpeded access -- including across conflict lines within Sudan," said UN Secretary General Antonio Guterres's spokesman Stephane Dujarric.

"A massive mobilization of resources from the international community is also critical," he added.

The UN's World Food Programme has warned that the war risks "triggering the world's largest hunger crisis."

Jill Lawler, the emergency chief in Sudan for the UN children's agency UNICEF, said there were enough aid stocks in Port Sudan, but the problem was getting the aid from there to the people in need.

Lawler said she last week had led the first UN mission to reach Khartoum state since war erupted 11 months ago.

They had seen first-hand that "the scale and magnitude of needs for children across the country are simply staggering," she told reporters in Geneva via video link from New York.

The war "is pushing the country towards a famine" with hunger "the number one concern people expressed."

- 'Moment of truth' -

Mandeep O'Brien, UNICEF representative in Sudan, said 14 million children needed humanitarian aid and four million were displaced.

There was only a "small window left to prevent mass loss of children's lives and future," she warned on X, formerly Twitter.

World Health Organization regional director Hanan Balkhy, who recently returned from a trip to Sudan, underlined the acute needs in Darfur, saying most health facilities were looted, damaged or destroyed.

Griffiths, the UN aid chief, lamented that fighting continued to rage during the Muslim holy month of Ramadan despite a Security Council resolution calling for a cessation of hostilities.

"This is a moment of truth," he wrote on X, formerly Twitter. "The parties must silence the guns, protect civilians and ensure humanitarian access."

The UN on Friday called for more financial support for aid operations in Sudan.

UN spokeswoman Alessandra Vellucci told reporters in Geneva that the world body had appealed for $2.7 billion to provide aid this year, but had received just five percent of that amount so far.