Sudan's military chief has confirmed the army's withdrawal from its last western stronghold of el-Fasher after the paramilitary Rapid Support Forces (RSF) declared control of the city.

In a televised address, Gen Abdel Fattah al-Burhan said he had approved the withdrawal in response to the "systematic destruction and killing of civilians".

He said he had agreed with local leaders to "leave and go to a safe place to protect the remaining citizens and the rest of the city from destruction".

The UN has raised the alarm over reports of atrocities committed by the RSF in recent days, and has called for safe passage for trapped civilians.

The RSF have denied accusations they were killing civilians.

The fall of el-Fasher could mark a significant turning point in Sudan's civil war, which has killed tens of thousands and displaced nearly 12 million people since April 2023.

The city's capture gives the RSF control over all five state capitals in Darfur, consolidating its parallel administration in Nyala, the capital of South Darfur.

On Monday, the UN head, Antonio Guterres, said he was "gravely concerned" over the situation in el-Fasher, and condemned the reported "violations of international humanitarian law".

He said the 18-month siege of el-Fasher - and the surrounding North Darfur region - have been an epicentre of suffering, with malnutrition, disease and violence claiming lives every day.

The UN Human Rights Office also warned that the number of large-scale, ethnically motivated violations and atrocities in el-Fasher was increasing.

"States with influence must act to prevent atrocities by RSF and allied fighters; accountability is key," it said in a statement.

In his address, Gen Burhan denounced inaction by the international community to end atrocities, and vowed to fight "until this land is purified".

"We can turn the tables every time, and we can return every land desecrated by these traitors to the nation's fold," he said.

El-Fasher was the army's last foothold in the vast western region of Darfur and had since May last year endured a worsening siege, causing a severe shortage of food.