Soldiers and gunmen from the paramilitary Rapid Support Forces (RSF) shot at each other on Friday in residential areas of the north, west and centre of the city, including during the call for special early morning Eid prayers, witnesses said.

The unabated fighting has killed hundreds of people and undermined an effort by United Nations Secretary General Antonio Guterres to broker a temporary truce over the three day holiday and allow civilians to reach safety.

In the absence of a ceasefire, foreign nations including the United States have been unable to evacuate their citizens from Sudan.

Army chief General Abdel Fattah al-Burhan on Thursday said he saw "no other option but the military solution" to the power struggle with the paramilitary force that erupted into violence last weekend.

The conflict between two previously allied leaders of the ruling military junta, army chief Burhan and RSF leader General Mohamed Hamdan Dagalo, also known as Hemedti, risks drawing in Sudan's neighbours and could play into regional competition between Russia and the United States.

The thud of heavy weaponry could also be heard across the Khartoum and its sister cities, together one of Africa's biggest urban areas. Army troops brandishing semi-automatic weapons were greeted by cheers on one street, footage released by the military on Friday showed.

Reuters verified the location of the video, in the north of the city, but could not immediately verify when it was filmed.

The World Health Organisation said at least 413 people have already been killed and thousands injured in the conflict, which has tipped Sudan into a humanitarian disaster, with hospitals under attack and up to 20,000 people fleeing into neighbouring Chad.

Even before the conflict, about a quarter of Sudan's people were facing acute hunger. The UN World Food Program halted its Sudan operation, one of its largest, on Saturday after three of its workers were killed.

The violence was triggered by disagreement over an internationally backed plan to form a new civilian government four years after the fall of autocrat Omar al-Bashir to mass protests, and two years after a military coup.

Both sides accuse the other of thwarting the transition.

The RSF condemned the military for what it said was new assaults.

"At this moment, when citizens are preparing to receive the first day of Eid al-Fitr, the neighbourhoods of Khartoum are waking up to the bombings of aircraft and heavy artillery in a sweeping attack that is directly targeting residential neighbourhoods," the RSF said early on Friday.

Thousands of civilians streamed out of Khartoum as gunfire and explosions sounded on Thursday. Large numbers also crossed into Chad to flee fighting in the western region of Darfur.

In El Fasher in North Darfur, a maternity hospital repurposed to treat casualties from fighting was overwhelmed and rapidly running out of supplies, said Cyrus Paye, coordinator for aid group MSF which supports the facility. All other hospitals in the city were closed.

Most of the 279 wounded patients the hospital received since Saturday were civilians hit by stray bullets, many of them children, and 44 have died, he said.

Another doctors' group said at least 26 people were killed and 33 were wounded El-Obeid city, west of Khartoum, on Thursday. Witnesses there described clashes and widespread looting.

Guterres, speaking to reporters after meeting virtually with the heads of the African Union, the Arab League and other organisations on Thursday, said: "There was a strong consensus on condemning ongoing fighting in Sudan and calling for cessation of hostilities as an immediate priority".

He said trapped civilians should be allowed to seek medical treatment, food and other supplies. The US endorsed the ceasefire proposal.

Burhan told Al Jazeera he would support a truce on condition it allowed citizens to move freely, which he said the RSF had prevented.

Australian Associated Press