The UN has called for safe passage for trapped civilians out of the Sudanese city of el-Fasher after paramilitary fighters announced they had seized control of the army's main base there.


Sudan's military has not acknowledged loss of the site, which would be a significant victory for the Rapid Support Forces (RSF) in the ongoing civil war.


UN chief António Guterres said the latest fighting marked a terrible escalation in the conflict, adding that the suffering of civilians was unbearable, AFP news agency reports.


El-Fasher is the last army foothold in the vast western region of Darfur and has been besieged by the RSF and its allies for 18 months.


Heavy fighting has been reported since Saturday after RSF fighters captured the home of the North Darfur governor.


UN Human rights chief Volker Türk warned that the risk of further large-scale, ethnically motivated violations and atrocities in el-Fasher is mounting by the day.


The RSF has been accused of targeting civilians in airstrikes and trapping nearly 250,000 people after encircling the city with an earth wall, leaving many on the brink of starvation.


The city is one of the worst battlegrounds of Sudan's civil war, leading the UN to call it an epicentre of suffering.


Tom Fletcher, the UN's top humanitarian official, stated that civilians must be allowed safe passage and access to aid, while the US is also urging for a ceasefire.