Prominent human rights lawyer Amal Clooney called for swift legal action to tackle the Islamic State group, also called ISIS, as she spoke about international crimes in Iraq and Syria during a discussion Wednesday in London.

The 39-year-old represents a number of victims of the genocide against the Yazidi people in Iraq, including ISIS rape survivor Nadia Murad, who was nominated for the Nobel Peace Prize last year and won a number of human rights awards. She was also named the United Nations goodwill ambassador.

Read: ISIS Carrying Out Genocide Of Yazidis, Amal Clooney Says Before Appearing At The UN

During the discussion at the Royal Institute of International Affairs at Chatham House, Clooney was joined by U.N. High Commissioner for Human Rights Zeid Raad Al Hussein and German federal prosecutor Christian Ritscher to talk about accountability.

Clooney called for collection of evidence against ISIS, which she said was responsible for “the worst crimes of our generation,” the Guardian reported. She has been involved in the collection of records and testimonies from survivors of the Yazidi community, many of whom she represents, to bring ISIS to justice over the heinous crimes and human rights violations carried out by the terrorist organization.

The barrister discussed instances where the men and women of the community were separated, so that ISIS fighters could allegedly shoot and kill the men, and rape and sell the women through slave markets. Clooney also talked about the discovery of almost 50 mass graves.

“All of this evidence is going to be lost if it’s not collected soon,” she said at the event. “Mass graves are being contaminated as relatives dig for remains of their loved ones. Documents are not being gathered. Witnesses are being dispersed around the world. They are increasingly reluctant to speak about these cases.”

The event took place weeks after Clooney addressed the U.N. and asked for an investigation into the Yazidi genocide carried out by the extremist group.