The city's last functioning hospital has been bombed over 30 times. Between 30 and 40 severely malnourished children arrive every day, seeking help. There's nothing to give them but animal feed.

"Even we're eating animal feed," said Dr Omar Selik, tilting his camera during a video call to show his meal: a sludgy paste made from pressed peanuts that is usually given to cows, camels and donkeys. "There's nothing else."

El Fasher is the worst battleground of Sudan's brutal civil war. For nearly 18 months the city, in the western region of Darfur, has been under siege by paramilitaries trying to starve it into submission. Fighters have erected a 30km earthen wall around its boundaries.

That leaves residents with a dire set of choices. Stay, and risk being bombed or starved. Run, and risk being killed, robbed or sexually assaulted.

"People seem to have forgotten us," said Dr Selik, breaking into tears as he spoke. "Oh my God, it's a very painful story."

The war in Sudan started more than two years ago, when clashes broke out between Sudan's army and its paramilitary rival, the Rapid Support Forces. The fight has engulfed Africa's third-largest country, forcing about 12 million people from their homes, killing tens of thousands and setting off a major famine. Aid groups call it the world's biggest humanitarian crisis.

Since March, when the Rapid Support Forces was expelled from the capital, Khartoum, the group has redoubled its effort to capture Darfur, the vast region in western Sudan where most RSF fighters are from. El Fasher is the last city in their way.

More than 500,000 people have fled El Fasher since April, when the RSF rampaged through Zamzam, a famine-stricken camp 11km south of the city, killing between 300 and 1,500 people in what the UN described as one of the worst massacres of the war.

A month later, the RSF began to circle the city with the giant earthen berm, according to satellite images published by the Yale School of Public Health. On August 27, construction to extend the berm was continuing.

Food convoys from the United Nations, which has not been able to deliver food to El Fasher in over a year, have been attacked by drones as they approached the city.

Now, doctors shelter in foxholes during bombing raids, and malnourished patients are sustained with animal feed, said Dr Suleman, who asked to be identified by one name because he has received death threats for his work.

The animal feed, known locally as ambaz, is a desperate solution, because it is prone to fungal contamination, especially in the rainy season. At least 18 residents have died in recent weeks after eating ambaz, local responders said.

"But there is no other option," Dr Suleman said.

New York Times News Service