GENEVA (Reuters) - Iraq must ensure that Islamic State leadership faces justice for alleged war crimes and genocide against civilians, not just charges of belonging to a terrorist group, a United Nations human rights investigator said on Thursday.

FILE PHOTO: Agnes Callamard, the U.N. Special Rapporteur on extrajudicial, summary or arbitrary executions, speaks at a news conference in San Salvador, El Salvador, February 5, 2018. REUTERS/Jose Cabezas/File Photo

Four men, two Iraqi and two Syrians, were sentenced to death by a Baghdad court on Oct 30 on charges of membership of Islamic State, a banned terrorist organization, Agnes Callamard, U.N. special rapporteur on extrajudicial, summary or arbitrary executions, said.

Their identity has not been revealed but she described them in a statement as “four senior affiliates of the ISIL leadership”, using a widespread acronym for the militant group.

“The trial should have shed light on the inner workings of ISIL and created a crucial judicial record of ISIL crimes against people.”

The jihadist group, which took large swathes of Iraq and Syria from 2014, declared a “caliphate” and imposed a reign of terror with public beheadings and sexual enslavement of women and girls including from the Iraqi Yazidi sect. It lost its last territorial stronghold in Syria last month.

“The Government of Iraq should take appropriate steps to prosecute the crimes perpetrated against the Iraqi people, including alleged genocide, crimes against humanity and war crimes,” Callamard said.

“At the very least, the Iraqi prosecutors should have brought additional charges from the Iraqi penal code, such as charges of murder, torture or disappearance, against the defendants, for the purpose of accountability,” she said.

International standards guaranteeing a fair trial appear not to have been met at the “hasty” criminal proceedings, during which the men were denied access to legal counsel, Callamard said.

Despite widespread violations, no victims or their families participated in the trial at Karkh criminal court or presented testimony, she said.

Callamard, who made recommendations about criminal accountability after a visit to Iraq in 2017, said on Thursday that the right to truth about gross human rights violations is an inalienable right.

“There is no justice delivered in secrecy,” she said.

“The trial of these four ISIL senior leaders should be an important opportunity for the victims, victims’ families, and witnesses to report on their ordeals and to be heard,” she said.