The paramilitary Rapid Support Forces (RSF) has been battling Sudan's army since April 2023 -- capturing El-Fasher, the last military stronghold in Darfur, western Sudan, in late October.

The takeover in Darfur was accompanied by reports of mass killings, sexual violence, abductions and looting, which led to increasingly vocal international calls for a ceasefire.

But the RSF victory in Darfur has allowed its forces to turn more attention to the oil-rich south.

One resident in El-Obeid, speaking to AFP anonymously for fear of reprisal, said they saw "smoke rising from the area" after a strike targeting the base of the army's 5th Division.

Another witness reported hearing a blast before "clouds of smoke" rose from the direction of the military base.

El-Obeid, about 400 kilometres (250 miles) southwest of Khartoum, hosts an airport and lies on a key supply route linking Darfur and the capital.

There has also been renewed fighting 400 kilometres southwest of El-Obeid in Babanusa -- the army's last remaining foothold in West Kordofan.

On Tuesday, the RSF released video footage appearing to show its fighters inside the base of the 22nd Infantry Division, the city's army headquarters.

A day earlier the group said it had secured "the liberation" of the entire city after repelling what it called a "surprise attack" by army units.

The army denied on Tuesday losing Babanusa, saying its forces had repelled a new RSF attack the previous day.

The army also accused the paramilitary force of launching daily drone and artillery strikes despite a unilateral ceasefire announcement by RSF leader Mohamed Hamdan Daglo.

Kordofan -- an area nearly the size of France -- has become a major battleground as the army seeks to push the RSF away from the vital highway linking the capital Khartoum to Darfur.

Meanwhile, international efforts to end the war have stalled.

Last month, US President Donald Trump vowed to seek peace after Saudi Crown Prince Mohamed bin Salman urged him to get involved.

Yet fighting has persisted.

On Monday, a war monitor accused the army of striking a nursing school in Kordofan's Komo village, killing at least 40 people, according to two residents who participated in the burials.