The Badush prison massacre was one of the worst crimes IS carried out after it seized control of a third of Iraq in a lightning offensive in 2014.

In June that year, IS fighters attacked the northwestern prison, freeing Sunni Muslims inmates and forcing 583 mainly Shiite prisoners into truck, before driving them to a ravine and shooting them.

In recent weeks, dozens of family members of the victims have given blood samples, which will be compared to the DNA of the remains, which were found in the mass graves in 2017.

"Thousands of families are waiting to know what happened to their relatives," Najm al-Jubburi, governor of the Nineveh province where the prison is located, told AFP.

The mass grave, discovered after Iraqi forces took control of the area in March 2017, is one of more than 200 the extremist group left behind in its rampage of brutality, according to the United Nations.

The remains of up to 12,000 people are believed to be buried in these graves, the UN says, which has accused IS of having committed genocide in Iraq.

One of those waiting for closure in Iraq is Abbas Mohammed, whose son was jailed at Badush following his arrest by US forces in 2005.

"After 17 years of not knowing whether my son is alive or dead, I need an answer," he told AFP.

Iraq has been struggling to identify remains of people from several violent episodes in its recent history, and is still discovering mass graves from the regime of executed dictator Saddam Hussein.

The task has been challenging, as remains have often been burned or exposed to the elements over the years.

"Work conditions are difficult," Saleh Ahmed, a member of government commission tasked with identifying the "martyrs", said at the site of the Badush mass grave.

"The heat is overwhelming. Some remains are entangled, and there are snakes and scorpions everywhere," he said, as 30 workers carried out the grim task of removing bodies from the grave.