More than 200 mass graves containing thousands of bodies have been found in areas of Iraq that were once controlled by the Islamic State (IS) group, a UN investigation has found.
The graves were found in the north and western governorates of Nineveh, Kirkuk, Salahuddin and Anbar.
They could contain as many as 12,000 victims, the UN report said.
IS seized parts of Iraq in 2014 and imposed brutal rule, commonly killing anyone of whom it disapproved.
It was eventually vanquished by a US-led air campaign backed by Iraqi government forces and allied militias on the ground, although pockets of IS activity remain in some areas.
The sites, the report notes, contain critical evidence that will not only identify the victims but also help prosecutors build cases for war crimes, crimes against humanity and possibly genocide.
The report said 202 mass graves had been documented so far, including 95 in Ninevah, 37 in Kirkuk, 36 in Salah al-Din and 24 in Anbar.
Investigators estimate between 6,000-12,000 victims are buried at the sites, including women, children, the elderly, people with disabilities, foreign workers, and members of the Iraqi security forces.
"The mass grave sites documented in our report are a testament to harrowing human loss, profound suffering and shocking cruelty," said Ján Kubiš, the UN Secretary General's special representative for Iraq.
"Determining the circumstances surrounding the significant loss of life will be an important step in the mourning process for families and their journey to secure their rights to truth and justice."
Significant challenges facing families of the missing are also highlighted. Currently, they have to register with five separate Iraqi offices to try to establish the fate of their loved ones.
The report calls for a public, centralised registry of missing persons as well as a federal Office of Missing Persons.
Iraq's war with IS
- January 2014: Forces of the Islamic State of Iraq and the Levant capture the cities of Falluja and Ramadi
- June 2014: The jihadists take Mosul, Iraq's second city, after a six-day battle
- 29 June 2014: ISIL changes its name to Islamic State, announcing a new caliphate under Abu Bakr al-Baghdadi
- August 2014: IS captures Sinjar. Some 200,000 civilians, mostly Yazidis, flee to the Sinjar mountains, prompting US-aided air drops
- March 2015: Iraqi forces and allied Shia militias retake Tikrit
- December 2015: Ramadi recaptured
- June 2016: Falluja retaken
- October 2016: Iraqi forces, Shia militias, Kurdish units and international allies lay siege to Mosul
- July 2017: Mosul retaken
- December 2017: Iraq's PM announces an end to the war with IS