UNITED NATIONS, Oct. 30 (Xinhua) -- Thousands of people remain trapped in Sudan's western city of El Fasher as reports of atrocities against civilians mount and the humanitarian crisis deepens, UN humanitarians said Thursday.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said it was alarmed by the atrocity reports in the capital of North Darfur state after the Rapid Support Forces (RSF) seized the city over the weekend.

"Local sources report widespread killings, abductions, maiming and sexual violence, alongside the detention and killing of aid workers," OCHA said. "Thousands of civilians remain trapped inside El Fasher, while many others are stranded at Garni, about 20 kilometers away, unable to flee due to insecurity and lack of transport."

The office said those still inside the city face life-threatening shortages of food, water and medical care. Aid workers are blocked from entering the city.

The UN Security Council on Thursday voiced grave concern over escalating violence in and around El Fasher and condemned the assault by the RSF on El Fasher and its devastating impact on the civilian population.

UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Tom Fletcher told the council that the situation in El Fasher has descended into "an even darker hell," with credible reports of widespread executions after RSF fighters entered the city.

OCHA said that civilians who managed to escape El Fasher are sheltering in the open in the localities of Kebkabiya, Melit and Tawila, where families lack necessities.

"Conditions in Tawila are particularly dire," the office said. "Safe water meets less than half of daily needs, markets have collapsed, and supplies of food, fuel and medicines are nearly exhausted. Diseases are spreading."

A UN-led assessment screened 715 displaced children and found nearly 60 percent of them to be acutely malnourished.

OCHA said the world body and its partners are scaling up response efforts despite enormous security and access challenges.

In Tawila, mobile health clinics are providing urgent medical and nutrition services for the newly arrived. Humanitarian partners have established health and nutrition sites, distributed reproductive health and cholera kits, and pre-positioned more than 8,000 cartons of therapeutic food, with another 6,000 cartons en route.

OCHA said that more than 30 nutrition sites remain operational, while community kitchens, cash distributions and temporary shelters continue to support newly displaced families. Psychosocial activities for children affected by trauma are to begin this week.

"The United Nations and partners are also sustaining water, sanitation and hygiene operations across Tawila, Melit and surrounding areas, trucking safe water, installing latrines, distributing hygiene kits, and conducting cholera prevention campaigns," the office said.

OCHA warned that explosive ordnance contamination continues to endanger civilians and humanitarian workers in and around El Fasher, limiting safe movement and delaying assistance. Sustained access for mine action teams and equipment is urgently needed to survey and clear hazardous areas.

The office reiterated its call for all parties to immediately halt hostilities, protect civilians and aid workers, and ensure sustained, unhindered humanitarian access.