At his first news conference since becoming the UN's top human rights official last month, Zeid focused on the "two monumental crises" that he said would inevitably cost nations many billions to overcome.
"The twin plagues of Ebola and ISIL," he told reporters, using an acronym for the group, "both fomented quietly, neglected by a world that knew they existed but misread their terrible potential before exploding into the global consciousness during the latter months of 2014."
Along the border of Iraq and Syria, the Islamic fighters who are seizing ground represent "a diabolical, potentially genocidal movement" that is the product of "a perverse and lethal marriage of a new form of nihilism with the digital age," he said.
The veteran diplomat and prince from Jordan also urged Iraq to join The Hague-based International Criminal Court and to take the "immediate step" of accepting its jurisdiction to allow for the prosecution of alleged war crimes and crimes against humanity that a UN Human Rights Council-appointed mission is investigating.