"We need to be very vigilant because especially history tells us, in particular in Europe, that the vilification of the other, that the denigration of the other, is a harbinger for what's to come," Volker Turk told reporters at a press conference in Geneva. "It's an alarm bell we need to ring", Reuters reported.
Far-right parties made gains in the European Parliament last month and France is holding a run-off election this weekend where opponents of its far-right, anti-immigrant National Rally are seeking to block them from power.
Turk, who is nearly half way through his four-year term as UN rights chief and whose job it is to speak out against the backsliding of freedoms, has fought for years to boost refugee protections.
As an Austrian, whose country became a hotbed of anti-semitism in the 1930s and participated in the Holocaust after its annexation by Nazi Germany in 1938, he has previously cited a desire to prevent future atrocities as part of his inspiration.
"In Europe we have unfortunately seen an increase in hate speech, an increase in discriminatory speech and it's important that political leaders are very clear that there should be zero tolerance for hate speech and for any attempt to denigrate others," he said.
SD/PR