Abdalla Hamdok speaks during a press conference on Sunday. Reuters

Hamdon described the humanitarian situation in Sudan as "catastrophic." He also warned of a possible regional conflict if the fighting escalates. "Shooting must stop immediately,” earlier he said in a video appeal to both sides posted on his Twitter account.

Fierce fighting raged in Sudan's capital despite an hours-long pause Sunday to address humanitarian needs including the evacuation of wounded, on the second day of battles that left three UN staff among more than 60 civilians killed throughout the country.

The World Food Programme said it was suspending operations in the impoverished country after the killing of its three workers.

The battles between the powerful armed forces and the Rapid Support Forces (RSF) sparked an international outcry and regional concern, including border closures by neighbours Egypt and Chad.

Deafening explosions and intense gunfire rattled buildings in the capital Khartoum's densely-populated northern and southern suburbs as tanks rumbled on the streets and fighter jets roared overhead, witnesses said.

Fighting continued after nightfall on Sunday, as Sudanese hunkered down in their homes with fears of a prolonged conflict that could plunge the country into deeper chaos, dashing long-held hopes for a transition to civilian-led democracy.

Violence erupted early on Saturday following weeks of power struggles between army chief Abdel Fattah Al Burhan and his deputy, Mohamed Hamdan Daglo who heads the heavily-armed RSF.

The pro-democracy Central Committee of Sudan Doctors reported 56 civilians killed as well as "tens of deaths" among security forces, and around 600 wounded.

Late on Sunday afternoon the army said they had "agreed to a United Nations proposal to open safe passage for humanitarian cases", including the evacuation of wounded, for three hours which ended at 1700 GMT.

RSF confirmed the measure, though they said it would last four hours, and both sides maintained their right to "respond in the event of transgressions" from the other side.

Despite the pause, heavy gunfire could still be heard in central Khartoum near the airport, and dense black smoke billowed from the surrounding area.

"The gunfire and explosions are incessant," Ahmed Hamid, 34, from a northern Khartoum suburb, said earlier.

Ahmed Seif, another Khartoum resident, called the situation very worrying and said: "It doesn't seem like it will calm any time soon."

Daglo's RSF say they have seized the presidential palace, Khartoum airport and other strategic locations, but the army insist they are still in control.

As the fighting continued, the stench of gunpowder wafted through Khartoum's streets, deserted except for soldiers.

Medics pleaded for safe corridors for ambulances and a ceasefire to treat the victims because the streets were too dangerous for transporting casualties to hospital.

Agencies