Amal Clooney has urged Iraq and the world’s nations not to let Isis “get away with genocide”.

The human rights lawyer, who represents victims of Isis rapes and kidnappings, told a UN meeting that what’s “shocking” is not just the group’s brutality but the “passive” response by the world’s nations to the campaign to investigate its crimes and bring the perpetrators to justice.

She urged Iraq’s Prime Minister Haider al-Abadi to send a letter to the UN Security Council so it can vote to set up an investigation into crimes by the group in Iraq where Isis once controlled about 40 per cent of the country’s territory but is now being routed by government and coalition forces.

“Justice is what the victims want...” Ms Clooney, who is the wife of actor George Clooney, said, “but justice will be forever out of reach if we allow the evidence to disappear, if mass graves are not protected, if medical evidence is lost, if witnesses can no longer be traced.”

Ms ​Clooney expressed frustration that nothing has happened since she came to the UN six months ago seeking accountability for victims of Isis.

“Killing Isis on the battlefield is not enough,” she said. “We must kill the idea behind Isis by exposing the brutality and bringing individual criminals to justice.”

Ms Clooney represents Nadia Murad, a Yazidi woman captured by Isis in Iraq in 2014, who has spoken out since her release about being raped, sold as a sex slave, and praying for death while in captivity.

Ms Murad, now a goodwill ambassador for the UN Office on Drugs and Crime for the Dignity of Survivors of Human Trafficking, told the meeting that victims have patiently waited for over a year for the investigation of Isis to start “to be able to at least bury our dead”.

“Why it is taking so long?” she asked, her voice breaking with emotion. “I cannot understand why you are letting Isis get away with it, or what more you need to hear before you will act. So today, I ask the Iraqi government and the UN to establish an investigation and give all the victims of Isis the justice they deserve.”

Ms ​Clooney addressed Mr Abadi saying it was initially Iraq’s idea to involve the UN and sending a letter “would silence those who doubt your commitment to bring Daesh [Isis] to justice”.

If no letter is forthcoming, she said the Security Council could act without Iraq’s consent, or it could refer the extremist group to the International Criminal Court, or the General Assembly could establish “an accountability mechanism” as it did for crimes in Syria in December. UN secretary general Antonio Guterres could also launch an investigation, she said.

“But none of this has happened,” Ms Clooney said. “Instead, mass graves in Iraq lie unprotected and un-exhumed, witnesses are fleeing and not one Isis militant has faced trial for international crimes anywhere in the world.”

She urged all countries “to stand up for justice” and demonstrate “moral leadership” to make sure that Isis is held accountable.

Britain’s UN ambassador Matthew Rycroft told the meeting he looks forward to finalising the Security Council resolution with Iraq “very, very soon”. He said the aim is to assist Iraq “with the difficult but crucial challenge of preserving the huge amount of evidence of Daesh [Isis] crimes committed on Iraqi territory.”

In pictures: Isis' weapons factories Show all 11 1 /11 In pictures: Isis' weapons factories In pictures: Isis' weapons factories A mortar round fin manufactured by Isis in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis rocket components discovered in Gogjali, Mosul, Iraq in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortars discovered near Karamlais, Iraq, in November 2016 CAR In pictures: Isis' weapons factories An Isis rocket launch frame in Qaraqosh, November 2016 Conflict Armament Research In pictures: Isis' weapons factories A memo from Isis' COSQC on quality control at a manufacturing facility in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Electrically-operated initiators manufactured by Isis in forces Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortar tubes at a manufacturing facility in Karamlais, November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis mortar production facility discovered in Gogjali, Mosul, in November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis weapons manufacturing facilities near Mosul in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Stocks of French-manufactured Sorbitol, Latvian potassium nitrate and Lebanese sugar at an Isis weapons factory in Iraq Conflict Armament Research In pictures: Isis' weapons factories A destroyed Isis weapons facility in Qaraqosh, Iraq, November 2016 Conflict Armament Research

Iraq’s UN ambassador Mohamed Alhakim said the government plans to try cases involving low and mid-level members of Isis but it will have to work with the international community to bring the top leaders to justice.

He made no mention, however, of UN help in preserving evidence or the required letter.