Mobilisation around Kadugli, capital of South Kordofan state, comes after nearly 10 weeks of fighting focused in the capital, Khartoum, between Sudan's army and the paramilitary Rapid Support Forces (RSF).

The army on Wednesday accused the SPLM-N rebel group led by Abdelaziz al-Hilu, which controls parts of South Kordofan state, of breaking a long-standing ceasefire agreement and attacking an army unit in the city.

The army said it had fought back the incursion but sustained losses.

In the fighting between the army and the RSF, army air strikes on Thursday morning hit areas of southern Khartoum and the RSF responded with anti-aircraft weaponry, residents said.

The war since mid-April has uprooted more than 2.5 million people from their homes and threatened to destabilise neighbouring countries suffering from a combination of conflict, poverty and economic pressures.

South Kordofan has Sudan's main oil fields and borders West Darfur State as well as South Sudan.

The SPLM-N, which has strong ties to South Sudan, also attacked the army in the South Kordofan city of al-Dalanj on Wednesday, as did the RSF, residents said.

Residents of Kadugli said the army had redeployed forces to protect its positions in the city on Thursday, while the SPLM-N was gathering in areas on the outskirts.

There were electricity and communications outages as well as dwindling food and medical supplies, they said.

The war has also brought an eruption of violence in Darfur, with the West Darfur city of El Geneina worst hit.

Nyala, capital of South Darfur and one of Sudan's largest cities, has seen clashes between the army and RSF in recent days after a period of calm, amid electricity and communications blackouts.

In Al Fashir, capital of North Darfur, the army and the RSF deployed widely across the city on Thursday, appearing to prepare for combat and causing the closure of the main market, witnesses said.