The UN high commissioner for human rights took aim at US Republican front-runner Donald Trump on Friday, blasting the presidential candidate for promoting bigotry.

Zeid Raad al-Hussein made the remarks at Case Western Reserve University in Cleveland, Ohio, the same city where Republicans will meet in July to nominate their party's presidential candidate.

"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 told students in a speech.

"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," Zeid said.

Over the course of his campaign, Trump has said that "torture works" and said he would bring back techniques he called worse than waterboarding - a harsh interrogation method banned by the Obama administration.

Trump has also been criticized for his promise to build a wall on the US-Mexico border to keep out migrants and to ban Muslims from entering the US, ideas the human rights chief called "grossly irresponsible."

Though it did not refer to Trump by name, the message was clearly intended for the Republican front-runner. Zeid also admonished the "multiple candidates" who advocate surveillance and other invasive measures targeting Muslims.

"To casually toss this gasoline on the smoldering embers of fear is to risk great harm to a great nation. Discrimination is a powerful and profoundly destructive force," he said, adding that the world would be watching the upcoming convention in Cleveland.

"It is my deepest hope that the people of this country will demonstrate their profound understanding of human dignity and human rights," he said.

Trump is currently locked in a contentious primary battle with Texas Senator Ted Cruz, struggling to secure enough Republican delegates to win the nomination in Cleveland on the first ballot or risk a contested convention.

bw/cmk (AFP, Reuters)