UN chief Guterres 'gravely alarmed' by reports of RSF assault on al-Fashir in Sudan

United Nations Secretary-General Antonio Guterres is "gravely alarmed" by reports of a full-scale assault on the Sudanese city of al-Fashir by the paramilitary Rapid Support Forces (RSF) and called on its leader to halt the attack immediately, a UN spokesperson said on Saturday.

Guterres warned any further escalation threatens to spread the conflict throughout the country's western Darfur region, the spokesperson said.

"He calls on Lt. General Mohamed Hamdan 'Hemedti' Dagalo to act responsibly and immediately order a halt to the RSF attack," UN spokesperson Stephane Dujarric said in a statement. "It is unconscionable that the warring parties have repeatedly ignored calls for a cessation of hostilities."

War erupted in Sudan between the Sudanese army and the RSF in April last year, triggering the world's largest displacement crisis. UN officials have warned the worsening violence around al-Fashir threatens to unleash more inter-communal strife.

US national security adviser Jake Sullivan said on Saturday that the conflict will be on the agenda when President Joe Biden meets with United Arab Emirates President Sheikh Mohammed bin Zayed Al Nahyan on Monday.

Sudan and the United Arab Emirates have clashed at the UN Security Council over accusations by the army-aligned Sudanese government that the UAE is arming and supporting the RSF.

"We are concerned about a number of countries and the steps they are taking to perpetuate rather than resolve the conflict," Sullivan told reporters.

"Our ultimate objective is to get the entire conflict with Sudan on a different track than the tragic and horrific track it is on right now. And I think that requires some intense but sensitive diplomatic conversations with a number of players."

In a resolution adopted in June, the UN Security Council demanded a stop to the siege of al-Fashir - a city of 1.8 million people in Sudan's North Darfur region - by the RSF and an immediate end to fighting in the area.

The resolution also called for the withdrawal of all fighters who threaten the safety and security of civilians in al-Fashir, the last big city in the vast Darfur region not under RSF control.

In the early 2000s, the UN estimates some 300,000 people were killed in Darfur when "Janjaweed" militias - from which the RSF formed - helped the army crush a rebellion by mainly non-Arab groups.

Sudanese leaders are wanted by the International Criminal Court for genocide and crimes against humanity.