The United Nations’ top official for humanitarian aid made an emotional plea for peace in Syria, as he leaves office after a two-year tenure that has witnessed the prolonged destruction of a nation.

“As I leave the United Nations, despite every humanitarian’s best efforts, in the United Nations and beyond, none of us can escape a share in the shame that collectively we have not put a stop to this — despite at least 500,000 Syrians now killed, let alone millions injured, displaced, fled and petrified,” Stephen O’Brien told the Security Council on Wednesday.

“I call again – one final time as the Emergency Relief Coordinator – for members of this Council to urgently refer the situation and the people responsible for it in Syria to the International Criminal Court,” O’Brien said.

The war in Syria has claimed more than 500,000 lives and displaced millions, creating more than five million refugees, most of whom live in neighbouring countries, according to UN data.

It began when forces loyal to Bashar al-Assad cracked down on the opposition with disproportionate force. Things then spiraled out of control after the emergence of Daesh as a terrorist organization that claimed territory from Syria and Iraq to establish its so-called “caliphate”.

The suffering in Syria has been a major catalyst for mass migration in the region that triggered shockwaves around the world.