Khartoum/Sudan — Clashes, artillery fire and air strikes surged in Sudan's capital on Sunday, witnesses said, as a war between rival military factions that has displaced 2.5 million people and caused a humanitarian crisis entered its 11th week.

Witnesses also reported a sharp increase in violence in recent days in Nyala, the largest city in the western Darfur region. The U.N. raised the alarm on Saturday over ethnic targeting and the killing of people from the Masalit community in El Geneina in West Darfur.

Khartoum, the capital, and El Geneina have been worst affected by the war that broke out on April 15 between Sudan's army and the paramilitary Rapid Support Forces (RSF), though last week tensions and clashes escalated in other parts of Darfur and in Kordofan, in the south.

Fighting has intensified since a series of ceasefire deals agreed at talks led by the United States and Saudi Arabia in Jeddah failed to stick. The talks were adjourned last week.

Residents in the three cities that make up the wider capital - Khartoum, Bahri and Omdurman - reported fierce fighting from Saturday evening, continuing into Sunday morning.

The army, led by Abdel Fattah al-Burhan, has been using air strikes and heavy artillery to try to dislodge the RSF led by Mohamed Hamdan Dagalo, known as Hemedti, from neighbourhoods across the capital.