He told the U.N.'s annual commemoration of International Holocaust Remembrance Day that anti-Semitic incidents in the United States increased 57 percent in 2017, according to the Anti-Defamation League. He said the European Union's Fundamental Rights Agency reported last year that 28 percent of Jews experienced some form of harassment just for being Jewish.

The U.N. chief also pointed to attempts to rewrite the history of the Holocaust, during which 6 million Jews and many others were murdered by Adolf Hitler's forces during the Nazi occupation of Europe in World War II.

Guterres also warned that neo-Nazi group are proliferating and recruiting the disaffected and people with military experience.

The massacre three months ago at the Tree of Life synagogue in Pittsburgh by a heavily armed man shouting "All Jews must die" was in keeping with the neo-Nazis' "advocacy of violent, so-called 'lone wolf' attacks," the secretary-general said. The man killed 11 worshippers in the worst anti-Semitic attack in U.S. history.

"Inevitably, where there is anti-Semitism, no one else is safe," Guterres said. "Across the world, we are seeing a disturbing rise in other forms of bigotry."

He pointed to attacks and persecution aimed at Muslims in several countries, at Rohingya Muslims in Myanmar, at the Yazidi minority in Iraq, and at others, "simply for who they are."

"Intolerance today spreads at lightning speed across the internet and social media," Guterres said. "Perhaps most disturbingly, hate is moving into the mainstream — in liberal democracies and authoritarian systems alike."

He said political discourse is being coarsened and "the demonization of others rages on."

"Such hatred is easy to uncork, and very hard to put back in the bottle," he warned.

International Holocaust Remembrance Day marks the liberation of the Nazi's Auschwitz death camp 74 years ago, and Guterres said it is imperative to heed the lessons of the Holocaust, especially by keeping its memory alive.

But he cited a recent poll in Europe that said one-third of people surveyed reported knowing "little or nothing about the Holocaust." Among millennials, "some two-thirds had no idea Auschwitz was a death camp," he said.

"Education is crucial — about the Holocaust, about genocide and crimes against humanity, about racism and the history of slavery," Guterres said.

"And we must stand up to those who disseminate hatred," he said.