The U.N. High Commissioner for Human Rights launched a thinly veiled attack on U.S. Republican front-runner Donald Trump and other presidential hopefuls on Friday, in a speech titled "The road to violence."

"Bigotry is not proof of strong leadership. It is evidence of the lowest and most craven lack of faith in the principles that uphold a 'land of the free,' " Zeid Ra'ad al Hussein said in a speech at a U.S. university in Cleveland.

"Less than 150 miles away from where I speak, a front-running candidate to be President of this country declared, just a few months ago, his enthusiastic support for torture, . . . inflicting intolerable pain on people, in order to force them to deliver or invent information that they may not have.