Sudan's battling factions have both claimed to have made gains as continued violence cut power and water in the capital.
The rupture between the army and the paramilitary Rapid Support Forces (RSF) has killed at least 185 people and injured more than 1,800, according to the UN envoy to Sudan Volker Perthes.
Their deadly power struggle which has involved air strikes and fighting in the capital Khartoum according to residents has derailed a shift to civilian rule and raised fears of a wider conflict.
Mr Perthes said the two sides showed no signs of being willing to negotiate.
"The two sides who are fighting are not giving the impression that they want mediation for peace between them right away," Mr Perthes said.
He said the sides had agreed on a three-hour humanitarian truce.
But for a second consecutive day fighting continued despite the promises of calm, according to Al Jazeera and Al Arabiya TV reporters broadcasting from Khartoum.
The fighting in Khartoum and its adjoining sister cities of Omdurman and Bahri since Saturday (local time) is the worst in decades and risks tearing Sudan between two military factions that had shared power during a rocky political transition.
Army Chief General Abdel Fattah al-Burhan heads a ruling council installed after a 2021 coup and the 2019 ousting of veteran leader Omar Bashir during mass protests. RSF leader General Mohamed Hamdan Dagalo, known as Hemedti, is his deputy.
Under an internationally backed transition plan, the RSF was shortly due to merge with the army.
Discord over the timetable for that process delayed a framework deal for a civilian transition that was due to be signed earlier this month.
General Burhan on Monday branded the RSF a rebel group and ordered it be dissolved as the two sides exchanged bitter accusations.
In comments to Sky News, he said he was secure in a presidential guesthouse within the defence ministry compound.
RSF leader Hemedti, whose whereabouts since Saturday was unknown, called the army chief "a radical Islamist who is bombing civilians from the air".
Continued violence could destabilise a volatile region and play into competition for influence there between Russia and the United States, and among regional powers that have courted different actors in Sudan.
Egypt, which has long been wary of political change in Khartoum, is the most important backer of Sudan's armed forces. Hemedti has cultivated ties with several foreign powers including the United Arab Emirates and Russia.
The European Union said its envoy to Sudan was assaulted in his own residence on Monday but did not give any details. The White House said there were no plans yet for a US government evacuation.
There was no sign on Monday that either side was willing to back down. While the army is larger and has air power, the RSF is widely deployed inside neighbourhoods of Khartoum and other cities, giving neither faction the edge for a quick victory.
Fighting between the sides in Darfur has meanwhile raised the spectre of renewed conflict in the western region that from 2003 was plagued by years of bloody warfare that killed as many as 300,000 people and displaced 2.7 million.
Hospitals damaged in Sudan fighting
Offices, schools and petrol stations in the capital were shut on Monday, while health services were widely disrupted and a doctors' committee said most major hospitals had gone out of service.
The bridges linking Khartoum with Omdurman and Bahri across the Nile River's two main branches were blocked by armoured vehicles, and some roads leading from the capital were impassable. Television images showed a fire raging at the international airport inside the city.
With water and power also cut across large parts of the capital, some residents were venturing out to buy food, forming long queues at bakeries.
There has been no police presence on the streets of Khartoum since Saturday, and witnesses reported cases of looting.
"We're scared our store will be looted because there's no sense of security," said Abdalsalam Yassin, 33, a shopkeeper who had bought extra stock ahead of the coming Eid al-Fitr Holiday.
UN chief Antonio Guterres urged a return to calm, saying an already precarious humanitarian situation was now catastrophic and UN aid chief Martin Griffiths said fighting had shuttered many aid programmes.
'Life is paralysed': Calls for immediate ceasefire
Humanitarian aid organisation Islamic Relief — which has worked in Sudan since 1984 — is calling for an immediate ceasefire and for all parties to ensure that civilians and humanitarian workers are protected.
Islamic Relief's Sudan country director in Khartoum, Elsadig Elnour, said people are trapped in their homes and scared about what's to come.
"Life is paralysed, everything is closed and food supplies are running out," she said.
"Many of the poorest people don't have stocks of food, they buy whatever little they can afford each day — and now they can't even do that. Already critical levels of hunger in the country are now set to get even worse. Millions of people will need aid."
The calls have been made with the end of Ramadan in mind, Islam's holiest month.
Sudan has a majority Muslim population, and many in the country will begin Eid celebrations in a matter of days to mark the end of Ramadan.
Reuters/ABC
