Just after the cease-fire expired at 0400 GMT on Sunday, witnesses said clashes and artillery fire resumed in the north of Omdurman. They also reported fighting in southern and central Khartoum, and in Shambat along the Nile in Bahri up to the strategic Halfiya bridge, which crosses to Omdurman.
Witnesses said the fighting between the Sudan army led by Gen. Abdel Fattah al-Burhan and General Mohammed Dagalo's paramilitary Rapid Support Forces (RSF) was some of the heaviest for weeks.
"The truce made us relax a bit, but the war and fear are returning today," said Musab Saleh, a 38-year-old resident of southern Khartoum.
Mohamed Usher, a local activist who visited two sites of artillery shelling in southern Khartoum, said at least 11 civilians had been killed there. In East Khartoum, six civilians had been killed by the fighting, an activist in that area said.
Saudi Arabia and the U.S., which brokered the cease-fire at talks in Jeddah, said the truce had allowed delivery of some vital humanitarian assistance and confidence building measures.
"However, there were violations, and, following the expiration of the short-term cease-fire, facilitators have been deeply disappointed by the immediate resumption of intense violence, which we strongly condemn," they said in a statement.
Fighting has been concentrated in the capital, much of which has become a war zone plagued by looting and clashes. But unrest has also flared elsewhere including the western region of Darfur, already suffering from a conflict that peaked in the early 2000s.
Another affected city is El Obeid, capital of North Kordofan State southwest of Khartoum and on a major route to Darfur. Residents say it is under a state of siege due to the conflict, with supplies of food and medicine cut off.
The wider Kordofan region is an important agricultural area and source of livestock, oilseeds and gum arabic.
"The situation is difficult. The RSF are spread out on the roads between the villages and they are looting, and there are gangs looting everywhere. Moving from place to place became dangerous," North Kordofan resident Mohamed Salman told Reuters by phone.
"We don't know how we'll plant or how we'll live."
The RSF has said it is trying to counter looting, and has denied responsibility for the violence in Darfur.
Some 400,000 of those who have fled their homes have crossed into neighbouring countries, about half of them heading north to Egypt.
On Saturday, Egypt tightened entry rules by extending a requirement for entry visas from men aged 16-50 to all Sudanese citizens.
The conflict has killed hundreds of civilians and displaced more than 1.9 million, triggering a major humanitarian crisis that threatens to spill across a
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