Authorities in Iraq’s northern Nineveh province on Sunday launched the first phase of exhuming one of the largest mass graves of the Islamic State’s (ISIS) victims - the Khasfa pit. 

The Khasfa pit, located some 20 kilometers south of Mosul, was a natural sinkhole used by ISIS as an open mass grave. It is believed to contain the remains of around 4,000 victims. 

“Our teams have begun the first phase, which will last for 15 days. Our work includes collecting evidence and the bones and remains that are on the surface of the ground and around the grave area,” Ahmed Qusay al-Asadi, head of the initiative’s search and rescue team, told Rudaw. 

Asadi explained that numerous complexities, including the presence of unexploded bombs among the human remains and the presence of sulfur water, have hampered exhumation efforts. “A deep excavation of the grave requires international assistance, engineering teams, and civil defense,” he said. 

Nineveh Governor Abdulqadir al-Dakhil labeled the Khasfa pit as “one of the largest mass graves in human history.” 

“We will work to erect a memorial at this site or another location to commemorate the Khasfa martyrs,” Dakhil said.

ISIS swept through vast swathes of Iraq in 2014 and declared a so-called caliphate in a brazen offensive that saw the group take control of several Iraqi cities, including the second-largest northern city of Mosul. It was declared territorially defeated in 2017.  

During its brutal reign, the jihadists committed untold atrocities on non-Muslims and Shiite Muslims, such as genocide, sexual slavery, and massacres.

The remains of around 400,000 people are estimated to be in mass graves across Iraq, according to Human Rights Watch (HRW).