U.N. investigators are compiling evidence on the development and use of chemical weapons by Islamic State extremists in Iraq after they seized about a third of the country in 2014, and are advancing work on the militant group’s gender-based violence and crimes against children, Sunni and Shiite Muslims, Christians and Yazidis, the head of the investigative team said Wednesday.

Christian Ritscher told the U.N. Security Council that survivors of a March 2016 chemical attack against Taza Khurmatu, a mainly Shia Turkmen town south of Kirkuk in northeast Iraq, were still deeply impacted when he visited earlier this year.

He said he has prioritized the investigation of chemical weapons used by the Islamic State, also known as ISIL.

“ISIL weaponized several chemical agents and deployed these as chemical rockets and mortars, as well as improvised explosive devices, in the vicinity of Taza Khurmatu” which hit residential neighborhoods and agricultural fields, Ritscher said.

The attack against Taza Khurmatu was believed to be the first use of chemical weapons by ISIL, according to the U.N. investigators. They have said more than 6,000 residents were treated for injuries and two children died within days of exposure while many survivors continue to suffer chronic and ongoing effects.

Ritscher said his team’s investigation “has provided specialized insight and analysis on the munitions, remnants and materials that were recovered” in Taza Khurmatu.

“Significant volumes of battlefield evidence, including ISIL payroll records and correspondence, were discovered, allowing the team to identify persons of interest and establish links to potential senior ISIL members,” he said.

Islamic State fighters seized Iraqi cities and declared a self-styled caliphate in a large swath of territory in Syria and Iraq in 2014. The group was formally declared defeated in Iraq in 2017 following a three-year bloody battle that left tens of thousands dead and cities in ruins. However, its sleeper cells continue to stage attacks in different parts of Iraq.

The U.N. Investigative Team to Promote Accountability for Crimes committed by the Islamic State group, known as UNITAD, which Ritscher heads, was established by the Security Council in 2017 to collect evidence so perpetrators of crimes by the Islamic State can be held accountable at trials. It has worked closely with Iraqi judicial officials.

A UNITAD report in May 2021 said the Islamic State group “tested biological and chemical agents and conducted experiments on prisoners … causing death,” and an initial investigation was launched.

Ritscher assured the Security Council that “there is no shortage of evidence on ISIL crimes in Iraq, as ISIL was a large-scale bureaucracy that documented and maintained a state-like administrative system.”

He said his team has led efforts that have so far digitized 8 million pages of ISIL documents held by Iraqi authorities, including Kurdish officials, and as a next step UNITAD is establishing a central archive “that will be the unified repository of all digitized evidence against ISIL.”

Ritscher said UNITAD is also prioritizing “persons of interest” living in other countries and is currently supporting criminal proceedings against alleged members and supporters of ISIL in 17 countries.

(AP)