The New York-based Human Rights Watch (HRW) stated on Wednesday that the mass killing of 770 soldiers took place at Camp Speicher near the city of Tikrit back in June.
The leading international watchdog also says the number of slain Iraqi troops was several times higher than what was initially reported.
The HRW also says the new number is based on analysis of new satellite imagery, videos and a survivor’s account.
On June 10, the terrorists took hundreds of prisoners from a Mosul prison. They ordered the prisoners to get on their knees and then opened fire, killing up to 670 people on the spot.
UN deputy Human Rights Commissioner Flavia Pansieri said on Monday that the ISIL militants have carried out "acts of inhumanity on an unimaginable scale" across Iraq over the past few months.
The UK-based human rights group, Amnesty International, has also strongly condemned ISIL terrorists for committing "war crimes, including mass summary killings, beheadings, crucifixions, and abductions."
The ISIL terrorists have committed heinous crimes and threatened all communities, including Shias, Sunnis, Kurds, Christians and Izadi Kurds, during their advances in Iraq.
Senior Iraqi officials have blamed Saudi Arabia, Qatar and some Persian Gulf Arab states for the growing terrorism in their country.
The terrorist group has links with Saudi intelligence and is believed to be supported by the Israeli regime.
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