The United States announced sanctions on Thursday on three Sudanese Rapid Support Forces (RSF) commanders over their roles in the "horrific campaign" of the siege and capture of El-Fasher.
The US Treasury said the RSF carried out "ethnic killings, torture, starvation, and sexual violence" in the operation.
Earlier Thursday, the UN's independent fact-finding mission on Sudan said the siege and seizure of the city in Darfur bore "the hallmarks of genocide."
Its investigation concluded that the seizure last October had inflicted "three days of absolute horror," and called for those responsible to be brought to justice.
"The United States calls on the Rapid Support Forces to commit to a humanitarian ceasefire immediately," US Treasury Secretary Scott Bessent said in a statement.
"We will not tolerate this ongoing campaign of terror and senseless killing in Sudan."
The Treasury noted that the three sanctioned individuals were part of the RSF's 18-month siege of and eventual capture of El-Fasher.
They are RSF Brigadier General Elfateh Abdullah Idris Adam, Major General Gedo Hamdan Ahmed Mohamed and field commander Tijani Ibrahim Moussa Mohamed.
Bessent warned that Sudan's civil war risks further destabilizing the region, "creating conditions for terrorist groups to grow and threaten the safety and interests of the United States."
The UN probe into the takeover of El-Fasher -- after the 18-month siege -- concluded that thousands of people, particularly from the Zaghawa ethnic group, "were killed, raped or disappeared."