Fresh fighting between the Sudanese army and paramilitaries has engulfed the aid hub of Wad Madani, triggering a new exodus of already-displaced civilians.
Wad Madani about 170 km southeast of Khartoum in al-Jazirah state had been a safe haven for civilians fleeing intense fighting in the capital since April.
The attack by the Rapid Support Forces (RSF) and a takeover of the densely populated city could cause massive displacement and deepen a humanitarian crisis in areas directly affected by the conflict.
Sudan's army said it was trying to hold off the offensive as fighter jets flew overhead, clouds of black smoke rose and blasts were heard from the city's northern outskirts.
The conflict between the Sudanese army and RSF rebels has already displaced nearly 7 million people, left the capital in ruins and triggered waves of ethnically driven killings in Darfur.
Residents in Khartoum and other cities have reported rape, looting, arbitrary killing, and detention by RSF rebels.
On Friday, the rebels said their attack on Wad Madani was aimed at destroying army strongholds
The UN Office for the Coordination of Humanitarian Affairs (OCHA) announced that it had ordered “a suspension of all humanitarian field missions within and from al-Jazirah state... until further notice.”
According to the UN agency, more than 270,000 of Wad Madani’s 700,000 inhabitants are dependent on humanitarian aid.
The fighting reportedly forced shopkeepers to shut their businesses and civilians to flee on foot with anything they could carry, seeking safer areas.
Initially spared from the war, the agricultural state of al-Jazirah has in recent months seen rebels encroach on the region.
The fighting in Sudan began in mid-April over a power struggle between army chief, Abdel Fattah al-Burhan, and his former deputy, Mohamed Hamdan Dagalo, who commands the RSF.
According to a conservative estimate by the Armed Conflict Location and Event Data Project, the civil war has so far claimed the lives of more than 12,190 people and wounded thousands more.
Since April, more than 5.4 million people in Sudan are internally displaced, while about 1.3 million have fled abroad, the UN says.
Both sides have been accused of indiscriminate shelling of residential areas, as well as targeting, looting and harassing civilians.
The United Nations, the Arab League as well as many countries in the world have urged the opposing sides to show restraint and engage in dialog to end the hostilities.
The African country, home to 45 million people, is also dealing with a severe economic crisis and an inflation reaching 400 percent.