The enduring lesson of the Holocaust and that of the genocides that followed is that they occurred not simply because of the machinery of death, but because of the state-sanctioned incitement to hatred. As international tribunals have recognized, the Holocaust did not begin in the gas chambers; it began with words. These are the chilling facts of history.

This enduring lesson finds contemporary application in the state-sanctioned incitement to genocide whose epicenter is President Mahmoud Ahmadinejad’s Iran. I take care to distinguish Ahmadinejad’s Iran from the peoples of Iran, who are themselves increasingly the target of the Iranian regime’s massive repression of human rights.

In Ahmadinejad’s Iran, a toxic convergence of the advocacy of the most horrific of crimes is embedded in the most virulent of hatreds. It is dramatized by the parading in Teheran streets a Shihab-3 missile draped in the words “Wipe Israel off the map,” while assembled thousands are exhorted to chants of “Death to Israel.”

Ahmadinejad’s Iran is increasingly resorting to incendiary and demonizing language, including epidemiological metaphors reminiscent of Nazi and Rwandan provocation. As minister of justice in Canada and involved in the prosecution of Rwandan incitement, I believe the precursors of provocation in Iran are more threatening than were those in Rwanda.

Indeed, President Barack Obama himself has declared that Ahmadinejad’s “words contain a chilling echo of some of the world’s most despicable and tragic history.” For example, Ahmadinejad and his officials characterize Israel as “filthy bacteria,” “a stinking corpse” and “a cancerous tumor that needs to be excised,” while referring to Jews as “evil incarnate,” “blood-thirsty barbarians” and the “defilers of Islam” — the whole as prologue to, and justification for, a Middle East genocide, while at the same time denying the Nazi one.

Crucially, Obama has made the important connection between Iran as the world’s leading state sponsor of terrorism, Iran as an inciter of hate and genocide against Israel, and Iran as an illegally developing nuclear power. He concluded that “all those things create the possibility of destabilizing the region and are not only contrary to our interests, but I think are contrary to the interests of international peace.”

As a state party to the Genocide Convention, the United States has not only the option but the obligation to take action to prevent genocide. A careful review of the evidence recently led a group of over 40 eminent international jurists, including former U.N. High Commissioner for Human Rights Louise Arbour and various law school deans, to conclude that Iran should be held to account for its hateful incitement to genocide, as prohibited under international law.

A former law professor, Obama should recognize the importance of taking action against genocidal incitement as the generic threat. This strategy directly addresses the root problem at issue — Iran’s destructive intentions — which have been overtly and repeatedly declared by senior members of the Iranian government, including Supreme Leader Ali Khamenei, who has said, “There is only one solution to the Middle East problem, namely the annihilation and destruction of the Jewish state,” and former President Akbar Hashemi Rafsanjani, who has declared, “even one atomic bomb inside Israel will wipe it off the face of the earth.”

Diplomacy targeted solely at Iran’s nuclear threat — as is presently the case — mistakenly ignores the terrifying and vilifying context in which that threat operates and, however inadvertently, sanitizes the provocation to genocide. When Obama engages Iran directly — a diplomatic strategy that I fully support — it is crucial that the illegal incitement to genocide so pervasive in Ahmadinejad’s Iran not be swept under the rug.

By calling for an end to Iran’s deplorable terrorist support and state-sanctioned culture of hate, Obama can ensure that engagement will not be stymied by Iranian impunity.

• Irwin Cotler, a Canadian member of parliament and former minister of justice, speaks at Emory University’s Center for the Study of Law and Religion at 7:30 p.m. Monday.