The assistance will include food and drinking water, as well as malnutrition emergency screening and treatment for children.

It comes as estimates say that five million people inside Sudan suffer extreme hunger, with food lacking also in neighboring countries where two million Sudanese have fled.

"We need the world to wake up to the catastrophe happening before our very eyes," Linda Thomas-Greenfield, the US ambassador to the United Nations, told reporters.

"We've seen mortality projections estimating that in excess of 2.5 million people -- about 15 percent of the population -- in Darfur and Kordofan, the hardest-hit regions, could die by the end of September," she said.

"This is the largest humanitarian crisis on the face of the planet, and yet somehow it threatens to get worse," she said, pointing to expectations that the key border crossing will become unpassable with the rainy season.

A UN humanitarian appeal for Sudan has received only 16 percent of its target, with much global attention focused instead on Gaza, where aid workers have also warned of famine risks.

Samantha Power, the administrator of the US Agency for International Development (USAID), said Sudan could be in worse shape than Somalia in 2011 when some 250,000 people died after three consecutive seasons without enough rain in a country grappling with near anarchy.

"The most worrying scenario would be that Sudan would become the deadliest famine since Ethiopia in the early 1980s," when as many as 1.2 million people died, she said.

Sudan descended into war in April 2023 when the generals in charge of the army and the paramilitary Rapid Support Forces (RSF) took up arms to seize control, rejecting a plan to integrate.

With the two sides battling for power across the country, Power said that deliveries of aid across the rival sides' lines of control was "virtually non-existent."

Power strongly criticized both sides. The RSF, she said, has been "systematically looting humanitarian warehouses, stealing food and livestock, destroying grain storage facilities and wells in the most vulnerable Sudanese communities."

The army, in turn "completely contradicts its commitments and its responsibility" to the Sudanese people by blocking aid from crossing the border with Chad into Darfur, she said.

"The really clear message here is that it is obstruction, not insufficient stocks of food, that is the driving force behind the historic and deadly levels of starvation in Sudan," she said.

"That has to change immediately."

- Diplomacy struggles -

Repeated US-led efforts to end the conflict have failed, with many observers concluding that the warring generals each think they can win on the ground.

A number of foreign powers have supported rival forces. Sudan expelled diplomats from the United Arab Emirates on allegations of fueling the RSF, while Egypt, Turkey and Iran have backed the army.

Recent fighting in El-Fasher, the last city in Darfur outside RSF control, has killed more than 220 people, according to charity Doctors Without Borders.

The UN Security Council on Thursday demanded that the RSF halt the siege, with all countries voting in favor except Russia, which abstained.

US Secretary of State Antony Blinken late last month called Sudan's army chief, General Abdel Fattah al-Burhan, and pressed both for humanitarian access and a resumption of diplomacy between the two sides.

Talks last year in the Saudi port city of Jeddah, brokered by the United States and Saudi Arabia, only briefly paused fighting, and a US push to restart the process has been unsuccessful.

"We know that there is no acceptable military solution to this conflict," Thomas-Greenfield said.

"We have been disappointed with the delays."