The UN High Commissioner for Human Rights has condemned the policies of US Republican presidential front-runner Donald Trump, equating them to bigotry.

Zeid Raad al-Hussein did not mention Trump by name, but he singled out the businessman's support of torture and his policies towards Muslims.

"Bigotry is not proof of strong leadership," Hussein said.

The commissioner also criticised a plan by rival candidate Ted Cruz to conduct surveillance on Muslim neighbourhoods.

"Hate speech, incitement and marginalisation of the 'other' are not a tittering form of entertainment, or a respectable vehicle for political profit," Hussein told an audience in Cleveland, Ohio.

He added: "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."

During the campaign, Trump has said that "torture works" and promised to bring back "a lot worse than waterboarding".

Waterboarding and other harsh interrogation techniques previously used by US forces on terror suspects have been banned by the Obama administration.

Trump's controversial statements have been criticised by world leaders including UK Prime Minister David Cameron, Mexican President Enrique Pena Nieto and Pope Francis.

Cameron called Trump's plan to ban Muslims from travelling to the US "divisive, stupid and wrong".

Both Pena Neito and the Pope have taken issue with Trump's call for a border wall between the US and Mexico.

Correspondents say Hussein's tough talk is unlikely to sway Trump. The New York billionaire has been a harsh critic of the UN on the campaign trail.

"The United Nations is not a friend of democracy," Trump told Israeli activists in March. "It's not a friend even to the United States of America, where as all know, it has its home. And it surely isn't a friend to Israel."