The United Nations Security Council on Thursday demanded a halt to the siege of al-Fashir - a city of 1.8 million people in Sudan's North Darfur region - by the paramilitary Rapid Support Forces (RSF) and an immediate end to fighting in the area.

The 15-member council adopted a British-drafted resolution that also calls for the withdrawal of all fighters who threaten the safety and security of civilians in al-Fashir, the last big city in the vast, western Darfur region not under RSF control.

"An attack on the city would be catastrophic," Britain's U.N. Ambassador Barbara Woodward told the council.

"This council has sent a strong signal to the parties to the conflict today. This brutal and unjust conflict needs to end."

War erupted in Sudan in April last year between the Sudanese army and the RSF, triggering the world's largest displacement crisis.

Top U.N. officials have warned the worsening violence around al-Fashir threatens to unleash bloody intercommunal strife throughout Darfur.

The British-drafted resolution received 14 votes in favour, while Russia abstained.

U.S. Ambassador to the U.N. Linda Thomas-Greenfield said it was a "precarious moment."

"The people of al-Fashir are trapped. They're surrounded by heavily-armed RSF. Food, water, medicine and other essentials are drying up," she said.

"Famine is setting in and the threat of further violence, including a large scale massacre, looms large."

Al-Fashir's main hospital has been attacked by the RSF and put out of service, Doctors Without Borders said on Sunday. Some 130,000 residents have fled the city due to fighting in April and May, the U.N. has said, but leaving is dangerous as those fleeing have been attacked on the main RSF-controlled road out.

The Security Council called on the warring parties to allow civilians to move to safer areas within and outside al-Fashir.

A June 5 report, opens new tab by the Yale Humanitarian Research Lab found some 40 settlements outside the city have been razed by arson since the end of March.

The Security Council urged countries "to refrain from external interference which seeks to foment conflict and instability ... and reminds all parties to the conflict and member states who facilitate the transfers of arms and military material to Darfur of their obligations to comply with the arms embargo measures."

U.N. sanctions monitors have described as "credible" accusations that the United Arab Emirates has provided military support to the RSF. The UAE has denied it.

The U.N. has said nearly 25 million people, half Sudan's population, need aid and some 8 million have fled their homes.

A United Nations-backed global authority on food security has said immediate action is needed to "prevent widespread death and total collapse of livelihoods and avert a catastrophic hunger crisis in Sudan."

The U.S. says the warring parties have committed war crimes and the RSF and allied militias have also committed crimes against humanity and ethnic cleansing.

Between 10,000 and 15,000 people were killed in one city alone in West Darfur last year in ethnic violence orchestrated by the RSF and allied Arab militia, according to a U.N. sanctions monitors report, seen by Reuters in January.