They reported combat in north Khartoum, and air strikes in the east of the capital, after the Saudi and U.S.-brokered cease-fire went into effect, the latest of multiple truces to have been announced and violated during five weeks of fighting.
A witness in southern Khartoum had reported an air strike, followed by silence, shortly before the cease-fire was to take effect.
A series of previous truce announcements were all violated by the warring generals, but the United States and Saudi Arabia — which brokered the deal — had said this one was different because it was "signed by the parties" and will be supported by a "cease-fire monitoring mechanism."
The deal, signed on Saturday by the army and the rival paramilitary Rapid Support Forces (RSF) after talks in the Saudi city of Jeddah, was due to come into effect on Monday evening with an internationally-supported monitoring mechanism. It also allows for the delivery of humanitarian aid.
According to the text of the Jeddah deal, a committee including three representatives from each of the warring parties, three from Saudi Arabia and three from the U.S. would monitor the cease-fire.
Repeated cease-fire announcements since the conflict started on April 15 have failed to stop the fighting, but the Jeddah deal marks the first time the sides have signed a truce agreement after negotiations.
The army and RSF reaffirmed their commitment to the cease-fire in statements on Sunday, even as fighting continued.
Analysts say it is unclear whether army chief Abdel Fattah al-Burhan or RSF commander Mohamed Hamdan Dagalo, known as Hemedti, are able to enforce a cease-fire on the ground. Both have previously indicated they are seeking victory in the war, and neither of them travelled to Jeddah.
The Jeddah talks focused on allowing in aid and restoring essential services. Mediators say further talks would be needed to seek the removal of forces from urban areas to broker a permanent peace deal with civilian involvement.
"The people of Khartoum are waiting for the truce and the opening of humanitarian corridors," said Mohamed Hamed, an activist in the capital. "The health situation is getting worse day after day."
Since the war began, 1.1 million people have fled their homes, moving either within Sudan or to neighboring countries, creating a humanitarian crisis that threatens to destabilize the region.
Millions of civilians have been trapped as the army has used air strikes and shelling to target the RSF forces that embedded themselves in residential areas early in the fighting.
Those still in Khartoum are struggling to survive amid mass looting, a collapse in health services, and dwindling supplies of food, fuel, power and water.
Safaa Ibrahim, a 35-year-old Khartoum resident, told Reuters by phone that she hoped the deal could bring an end to the conflict.
"We're tired of this war. We've been chased away from our homes, and the family has scattered between towns in Sudan and Egypt," she said. "We want to return to normal life and safety. Al-Burhan and Hemedti have to respect people's desire for life."
Since the conflict began, unrest has flared in other parts of Sudan, especially the western region of Darfur.
Some 705 people have been killed and at least 5,287 injured, according to the World Health Organization, though the true death toll is believed to be much higher.