Fighting between forces loyal to Sudan's rival generals on Friday rocked the western region of Darfur, witnesses said, on the fourth day of a fragile US- and Saudi-brokered ceasefire.
The one-week truce, the latest in a series of agreements that have all been systematically violated, was breached only minutes after it took effect on Monday night.
There have since been further violations of the ceasefire, which is meant to allow for much-needed humanitarian aid to reach war-ravaged parts of the country, with the warring sides blaming each other.
In El Fasher, the capital of North Darfur, residents reported "battles with all types of weapons", six weeks into a war between the regular army, led by Abdel Fattah al-Burhan, and the paramilitary Rapid Support Forces (RSF).
Since it erupted on April 15, the fighting has killed more than 1,800 people, according to the Armed Conflict Location and Event Data Project.
The United Nations says more than a million Sudanese have been displaced, in addition to 300,000 who have fled to neighbouring countries.
Even before the conflict began, one-third of Sudan's 45 million people faced famine, and about 25 million people were now in need of humanitarian aid, the UN said.
While the current ceasefire agreement has allowed for a lull in fighting, no humanitarian corridors have been opened to allow civilians to leave or aid to reach the affected areas.
The United States said on Thursday observers had detected the use of artillery, drones and military aircraft as well as fighting both in Khartoum and in Darfur.
"We retain our sanctions authority and if appropriate we will not hesitate to use that authority," said US State Department spokesman Matthew Miller.
Conditions have been particularly alarming in Darfur, already ravaged by a conflict that erupted in 2003 and saw then president Omar al-Bashir unleash the feared Janjaweed militia to crush a rebellion among ethnic minority groups.
The RSF, which is led by Burhan's former deputy Mohammed Hamdan Daglo, traces its origins to the Janjaweed.
Burhan and Daglo had in 2021 staged a coup that unseated a civilian transitional government but later fell out in a bitter power struggle.