Iraq asked for international help Wednesday to collect and preserve evidence of crimes by Islamic State militants and said it was working with Britain to draft a U.N. Security Council resolution to establish the investigation.
Britain, international human rights lawyer Amal Clooney and Nadia Murad, a woman from the Yazidi religious minority who was enslaved and raped by IS fighters in Mosul, have been pushing Iraq to allow a U.N. inquiry.
The 15-member Security Council could have established an inquiry without Iraq's consent, but Britain wanted Iraq's approval in a letter formally making the request. Iraq sent the letter, seen by Reuters, on Monday.
"We request assistance of the international community to get benefited from international expertise to criminalize Daesh terrorist entity," Iraqi Foreign Minister Ibrahim al-Jaafari wrote in the letter, which was translated from Arabic.
Daesh is another name for Islamic State, as is ISIS.
Britain's mission to the United Nations said on Twitter that it was working with Iraq on a draft resolution. It was not immediately clear when it could be put to a vote in the council.
IS's self-proclaimed caliphate effectively collapsed last month, when U.S.-backed Iraqi forces completed the recapture of Mosul, the militants' capital in northern Iraq, after a nine-month campaign.
Parts of Iraq and Syria remain under IS control, especially along the border.
"I hope that the Iraqi government's letter will mark the beginning of the end of impunity for genocide and other crimes that ISIS is committing in Iraq and around the world," Clooney said in a statement.
"Yazidis and other ISIS victims want justice in a court of law, and they deserve nothing less," Clooney said.
The Yazidis' beliefs combine elements of several ancient Middle Eastern religions. IS militants consider the Yazidis to be devil worshippers.
U.N. experts said in June last year that IS was committing genocide against the Yazidis in Syria and Iraq to destroy them through killings, sexual slavery and other crimes.
The Iraqi government said in the letter that it was important to bring IS militants to justice in Iraqi courts.