The United Nations secretary-general warned Tuesday that the war in Sudan is “spiraling out of control” after a paramilitary force seized the Darfur city of El Fasher.

Speaking at a UN summit in Qatar, António Guterres offered a stark warning about El Fasher and called for an immediate ceasefire in the two-year conflict that’s become one of the world’s worst humanitarian crises.

“Hundreds of thousands of civilians are trapped by this siege,” Guterres said. “People are dying of malnutrition, disease and violence. And we are hearing continued reports of violations of international humanitarian law and human rights.”

He added that there also were “credible reports of widespread executions since the Rapid Support Forces entered the city.”

UN officials have warned of a rampage by the paramilitary Rapid Support Forces after it took over the city of El Fasher, reportedly killing more than 450 people in a hospital and carrying out ethnically targeted killings of civilians and sexual assaults.

The RSF has denied committing atrocities, but testimonies from those fleeing, online videos and satellite images offer an apocalyptic vision of the aftermath of their attack. The full scope of the violence remains unclear because communications are poor in the region.

The RSF besieged El Fasher for 18 months, cutting off much of the food and other supplies needed by tens of thousands of people. Last week, the paramilitary group seized the city.

Asked if he thought there was a role for international peacekeepers in Sudan, Guterres said it was important to “gather all the international community and all those that have leverage in relation to Sudan to stop the fighting.”

“One thing that is essential to stop the fighting is to make sure that no more weapons come into Sudan,” he said. “We need to create mechanisms of accountability because the crimes that are being committed are so horrendous.”

The war between the RSF and the Sudanese military has been tearing apart Sudan since April 2023. More than 40,000 people have been killed, according to UN figures, but aid groups say the true death toll could be many times higher. The fighting has driven more than 14 million people from their homes and fueled disease outbreaks. Meanwhile, two regions of war-torn Sudan are enduring a famine that is at risk of spreading.

“It is clear that we need a ceasefire in Sudan,” Guterres said. “We need to stop this carnage that is absolutely intolerable.”