US Secretary of State Antony Blinken on Thursday warned Sudan's paramilitary force against what Washington called an "imminent large-scale attack" in North Darfur's capital, where thousands were seeking refuge from fighting.
"The United States is deeply troubled by reports of an imminent large-scale attack by Sudan's Rapid Support Forces (RSF) on El Fasher, North Darfur, that would subject civilians, including hundreds of thousands of displaced persons - many of whom only recently fled to El Fasher from other areas - to extreme danger," Blinken said in a statement.
"The United States calls on the warring parties to immediately cease further attacks in and around El Fasher," Blinken said.
While the United States did not cite the source of its information, the statement was unusually strong as it was issued in Blinken's name.
Since April, the war between regular forces loyal to army chief Abdel Fattah al-Burhan and the paramilitary RSF, commanded by his former deputy Mohamed Hamdan Daglo, has killed more than 9,000 people and displaced over 5.6 million.
The two sides returned to talks last week in Jeddah brokered by the United States and Saudi Arabia, but US officials say the goals for now are limited to pushing through ceasefires and allowing in humanitarian aid.
"At a time when so much hope is being placed on the Jeddah talks to achieve a sustainable ceasefire and facilitated humanitarian access, I call on all parties to refrain from escalating and expanding the conflict," said Clementine Nkweta-Salami, the United Nations' deputy special representative of the secretary-general for Sudan.
As negotiations proceed, violence has flared in Darfur, with an eyewitness in El Fasher telling AFP that an army base was targeted by drones Thursday.
The vast region of Darfur - the size of France and home to around a quarter of Sudan's 48 million people - is deeply scarred by a scorched-earth campaign launched two decades ago by the RSF's predecessor, the Janjaweed militia.
Then-president Omar al-Bashir used the Janjaweed to suppress non-Arab minorities - a bloody campaign that eventually saw him charged with genocide, war crimes and crimes against humanity by the International Criminal Court.
Civilians and international organisations warn history is repeating itself.
"I am alarmed by reports that civilians are being caught in the ongoing fighting," Nkweta-Salami said, "recalling the events in El Geneina in Darfur last June," when rights groups and witnesses reported massacres, rampant sexual violence and mass graves in the West Darfur capital.
The violence in El Geneina and other reports of ethnically-motivated killings by the RSF and allied militias triggered a new investigation from the ICC into alleged war crimes and crimes against humanity.