The area is home to hundreds of thousands of civilians who have fled the violence further north in the capital, Khartoum.

Dallia Abdelmoniem, who is currently in Cairo but has family in Wad Madani, told the BBC's Newsday programme about what happened at the military base.

"It's an army stronghold and the fact that the RSF was able to breach the army stronghold does not bode well," she said.

"It means that, first of all, the RSF is feeling more confident in their abilities, that the war is expanding. And this is a safe haven. It wasn't just a stronghold for the army. It's also a safe haven for the civilians who left Khartoum. So in terms of civilian safety, it's a catastrophe because they have no options, there's nowhere to go."

There's international concern that the war - which began in April - is spreading.

Over the weekend, the US State Department called on the RSF to cease its advance on Wad Madani.

Washington said the group's actions were inconsistent with its stated aim of protecting Sudanese civilians.

There are also reports of renewed fighting in the city of Nyala in Sudan's western Darfur region.