The head of a United Nations agency has called for an investigation into the killing of at least 87 people who were discovered in a mass grave in Sudan's West Darfur region.

United Nations High Commissioner for Human Rights Volker Türk has demanded a "prompt, thorough and independent investigation" into the grim discovery outside the region's capital El-Geneina.

Inside the mass grave were bodies of ethnic Masalit who along with other non-Arab communities are often targeted by Arab militias, supported by the RSF, according to Human Rights Watch.

The deceased were allegedly killed last month by the paramilitary Rapid Support Forces (RSF) and their allied militia.

"According to credible information gathered by the Office, those buried in the mass grave were killed by RSF and their allied militia around 13-21 June in El-Geneina's Al-Madaress and Al-Jamarek districts...," the UN body said in a statement Thursday.

The statement added that the bodies included individuals who were victims of the violence that occurred following the assassination of Khamis Abbaker, the Governor of West Darfur, on June 14.

Furthermore, the victims also include those who died due to untreated injuries.

Türk strongly condemned the killings and said he was "appalled by the callous and disrespectful way the dead, along with their families and communities, were treated."

"There must be a prompt, thorough and independent investigation into the killings, and those responsible must be held to account," Türk added.

He urged the Rapid Support Forces (RSF) and other parties involved in the conflict to abide by international law and facilitate prompt searches for the deceased, their collection, and evacuation, without discrimination based on ethnic background.

"The RSF's leadership and their allied militia as well as all parties to an armed conflict are required to ensure that the dead are properly handled, and their dignity protected," Türk stressed.

West Darfur remains one of the most conflict-ridden areas in the Sudanese Darfur region, with a long history of severe violence.

The recent killings reflect the atrocities committed during the early 2000s, where hundreds of thousands of people lost their lives in an ethnic cleansing campaign led by the Janjaweed, an Arab militia that preceded the RSF.