Much of Sudan has been gripped for nearly a year by a bloody war between the regular army and the paramilitary Rapid Support Forces.
"A fire broke out after a drone attack during an iftar," a witness said over the phone, referring to the evening fast-breaking meal during the Muslim holy month of Ramadan.
The meal, "organized by and at the base of the Islamist Baraa militia," which fights alongside the Sudanese army, "gathered both civilians and fighters," another resident told AFP.
Residents were gripped by a "wave of panic due to the shock of the explosion" in Atbara, some 300 kilometers (186 miles) northeast of Khartoum, the same source said.
The bodies of "12 killed and 30 injured" arrived at a hospital in Atbara, a medical source said, updating an earlier toll without specifying whether they were fighters or civilians.
The war, which broke out on April 15, has killed thousands and displaced more than 8.5 million people internally and across borders, according to the United Nations.
The fighting had spared Atbara, where army troops have been stationed to protect the city strategically located on the road to Port Sudan on the Red Sea, where the government loyal to the army has taken refuge.
No group immediately claimed the attack. The RSF owns drones but is located some 250 kilometres away from Atbara, on the roads leading out of the capital Khartoum.
The RSF originated from the feared Janjaweed militia that had been unleashed in the early 2000s by former dictator Omar al-Bashir to quash ethic tribes in Darfur.
The paramilitaries now control much of Darfur, a region the size of France that has been cut off from the rest of the country for months.
The new US envoy for Sudan, Tom Perriello, said military jets on Monday raided the city of El-Fasher in North Darfur, "where thousands of civilians from across Darfur have already fled."
Across the country, both the military and the RSF "continue to obstruct humanitarian assistance and the free movement of civilians," he wrote on X.