Report: Biggest mass grave by Daesh near Mosul with 4000 bodies

"Now, this natural depression five miles outside Mosul is believed to be the biggest mass grave in Iraq and the resting place of an estimated 4,000 bodies," Daily Telegraph reported.

The British media out let cited villagers, Iraqi police and human rights organizations as saying that ISIS has killed and buried security personnel in the natural depression five miles outside Mosul after the terrorist group captured the city in 2014.

Most victims were shot and dumped into the pit, witnesses said, while others perished in vehicles driven over the edge. Sinkhole was more than 400 meters deep before the dead began piling up

"Daesh (ISIS) would drive the victims to Khasfa in convoys of minibuses, trucks and pickups. The men had their hands bound and their eyes blindfolded. They were taken to the sinkhole and shot in the back of the head," said Mahmoud, a 40-year-old from the nearby village of Sananik who declined to give his full name for security reasons.

The dead would either tumble into the hole after being shot or be tossed into it by their masked killers, he said.

A grave containing the bodies of at least 300 members of the security forces was discovered last November on the outskirts of Hamman al Alil, a town about 30 kilometres from Mosul.

But the scale of the killing at Khasfa dwarfs all other known sites. "Khasfa is definitely one of the biggest, if not the biggest, mass grave by ISIS in Iraq.

The body count at Khasfa outstrips the most infamous massacre committed by IsiS– the murder of army cadets at the Camp Speicher military base near Tikrit.

ISIS terrorists butchered as many as 1,700 recruits in the June 2014 massacre, turning the water of the Tigris red with blood.

At Khasfa, 2,000 policemen and soldiers were murdered in one day alone, claimed Mahmoud, who said he was forced to watch mass executions by the terrorists on four separate occasions.

"In the beginning, you couldn't see the corpses at the bottom of the hole. Only later, when it began to fill up could you see the bodies," he said.

The victims of one of the executions he was forced to watch included his cousin, who worked as a police officer, he said.

On a separate occasion, he watched a bus full of bound and blindfolded Yazidi men being driven up to the lip of the sinkhole and then rolled over the edge.

Locals said the killing at Khasfa began six months after ISIS took Mosul, and that the terrorist group posted lists of those it had killed in local mosques.

Employees at a makeshift oil refinery just down the road from the sinkhole said they remembered seeing convoys of prisoners being ferried to the area and hearing gunfire from the same direction.

While the massacres continued, Human Rights Watch researchers were monitoring the sinkhole via satellite, and could see the pit filling up.

By June 2015, the terrorists had covered the hole with earth. Locals said ISIS pushed dozens of shipping containers into the hole, as well as concrete blast walls, before using bulldozers to cover it with earth.

Today, the Khasfa sinkhole is just a slight depression in the parched landscape, with little visible sign of the horrors beneath.