NEW YORK, Nov. 7 -- UN Secretary-General Antonio Guterres on Thursday warned against the danger of bringing extremism into mainstream politics across the world.

"In their quest for power, some political leaders are cynically bringing the loathsome views of extremist groups into the mainstream," Guterres told an event marking the 81st anniversary of Kristallnacht at the Museum of Jewish Heritage in New York City. "We see this in authoritarian regimes and liberal democracies alike."

Kristallnacht (Crystal Night), or the Night of Broken Glass, was a pogrom against Jews throughout Nazi Germany on Nov. 9-10, 1938.

"Decades after the Holocaust, the world's oldest hatred (of anti-Semitism) is still with us. Other forms of intolerance are also taking a deadly toll, from bombings at churches to massacres at mosques to assaults on migrants and refugees," said Guterres.

Hatred kills, but hatred also works in insidious ways to undermine relations between people and the foundations of society, he noted.

The online world has proven to be a boon for bigotry and violent misogyny. Terrorists and neo-Nazis are ramping up recruitment and radicalization. These groups post videos on the latest platforms and apps, often specifically designed to lure often unwitting young people. Their messages are filled with false promises of glory, and with real incitement targeting some of society's most vulnerable people, he said.

Parents, teachers and political leaders must all act with urgency before underground hatred becomes an overt and alarming new normal, said Guterres.

He also called for special attention to young people. "People are not born to hate. Intolerance is learned and so can be prevented and unlearned."