The United States on Monday implored all countries supplying weapons to Sudan's warring parties to halt arms sales, warning that history in the vast western Darfur region where there was a genocide 20 years ago “is repeating itself".

US Ambassador Linda Thomas-Greenfield told reporters after an emergency closed meeting of the U.N. Security Council that El Fasher, the only capital in Darfur not held by paramilitary forces, is “on the precipice of a large-scale massacre."

She urged all countries to raise the threat that “a crisis of epic proportions is brewing." Britain's deputy ambassador James Kariuki echoed her appeal saying: “The last thing Sudan needs is a further escalation on top of this conflict that's been going on for a whole year.”

Thomas-Greenfield said there are “credible reports” that the paramilitary Rapid Support Forces and their allied militias have razed many villages west of El Fasher and are planning “an imminent attack on El Fasher.”

“An attack on El Fasher would be a disaster on top of a disaster,” Thomas-Greenfield warned, saying it would put the two million people who live in El Fasher and 500,000 Sudanese who have sought refuge there at risk.

Thomas-Greenfield urged the paramilitary forces, known as the RSF, to end their siege of El Fasher “and swear off any attack on the city.”

She urged the RSF and rival government forces to take urgent steps to de-escalate the violence and engage in direct negotiations, protect civilians and enable humanitarian access, especially to the 5 million Sudanese “on the brink of famine” and 10 million others in desperate need of aid.

Sudan plunged into chaos in mid-April 2023, when long-simmering tensions between its military, led by Gen. Abdel Fattah Burhan, and the RSF paramilitary commanded by Mohammed Hamdan Dagalo broke out into street battles in the capital, Khartoum. Fighting has spread to other parts of the country, especially urban areas and the Darfur region.

UN political chief Rosemary DiCarlo told the council on April 19 the year-long war has been fuelled by weapons from foreign supporters who continue to flout UN sanctions aimed at helping end the conflict. “This is illegal, it is immoral, and it must stop,” she said.

She didn't name any of the foreign supporters.

But Burhan, who led a military takeover of Sudan in 2021, is a close ally of neighbouring Egypt and its president, former army chief Abdel-Fattah el-Sissi. In February, Sudan's foreign minister held talks in Tehran with his Iranian counterpart amid unconfirmed reports of drone purchases for government forces.

Dagalo, the leader of the RSF, has reportedly received support from Russia's Wagner mercenary group. UN experts said in a recent report that the RSF has also received support from Arab allied communities and new military supply lines running through Chad, Libya and South Sudan.

Thomas-Greenfield said Monday that all regional powers must stop providing weapons to the warring parties as the UN arms embargo demands, and told reporters the United States will continue pressuring them.

In response to a question, she said one of the countries the United States has engaged with is the United Arab Emirates, which has repeatedly denied providing any weapons to Sudan.

The UN's DiCarlo painted a dire picture of the war's impact — over 14,000 dead, tens of thousands wounded, looming famine with 25 million people in need of life-saving assistance, and over 8.6 million forced to flee their homes.

During the war, the Arab-dominated RSF have carried out brutal attacks in Darfur on ethnic African civilians, especially the ethnic Masalit, and have taken control of most of the vast region – with El Fasher its newest target.

Two decades ago, Darfur became synonymous with genocide and war crimes, particularly by the notorious Janjaweed Arab militias, against populations that identify as Central or East African. Up to 300,000 people were killed and 2.7 million were driven from their homes.

That legacy appears to have returned, with the International Criminal Court's prosecutor, Karim Khan, saying in January there are grounds to believe both sides may be committing war crimes, crimes against humanity or genocide in Darfur.

The RSF were formed from Janjaweed fighters by former Sudanese President Omar al-Bashir, who ruled the country for three decades before being overthrown during a popular uprising in 2019. He is wanted by the ICC on charges of genocide and other crimes during the conflict in Darfur in the 2000s.