The army blocked civilians from entering the city of Wad Madani — 180 kilometers (110 miles) south of the capital Khartoum — which had quickly become a safe haven when conflict broke out between the Sudanese armed forces and the paramilitary Rapid Support Forces on April 15.
An AFP correspondent saw fighter jets overhead and clouds of black smoke rising as blasts were heard from the city's northern outskirts.
Wad Madani is the capital of Al Jazira state, where half a million displaced people have sought refuge, according to the United Nations.
Initially spared from the conflict, the agricultural state has in recent months seen fighters encroach on the region, mobilizing troops and setting up checkpoints along the line of villages between Khartoum and Wad Madani.
The war between army chief Abdel Fattah al-Burhan and his former deputy, commander Mohamed Hamdan Dagalo, has claimed more than 12,190 lives, according to a conservative estimate by the Armed Conflict Location and Event Data Project.
Over 5.4 million people are internally displaced, according to the U.N., in addition to nearly 1.5 million who have fled across borders.
In a bleak reminder of the first days of the war in Khartoum, shops and businesses were quickly boarded shut Friday as families took to the streets "with anything they could carry," AFP's correspondent said, struggling to find transportation south.
In a statement, the Rapid Support Forces sought to "assure dear citizens" in Al Jazira and Wad Madani that "the goal of our forces is to destroy the strongholds" of the army.
Both sides have been accused of indiscriminate shelling of residential areas, as well as targeting, looting and harassing civilians.
'Hunger catastrophe'
The millions displaced across Sudan combined with the lack of good harvests, means hunger stalks large parts of the country.
The World Food Program warned on Wednesday that Sudan faces a "hunger catastrophe" if it cannot deliver regular food aid there.
"Parts of war-ravaged Sudan are at a high risk of slipping into catastrophic hunger conditions by next year's lean season," the WFP said in a statement.
It said this could happen if the U.N. agency is unable to expand access and deliver regular food assistance to people trapped in conflict hotspots including the capital Khartoum.
"Nearly 18 million people across Sudan are facing acute hunger ... more than double the number at the same time a year ago," the WFP said.