Former Mexican president Vicente Fox called Donald Trump “crazy” and lashed out at the US presidential candidate’s demand for Mexico to pay for a border wall.

“I am not going to pay for that f***ing wall. He should pay for it. He’s got the money,” Mr Fox told Fusion in an excerpt of the interview on the US television network’s website.

Mr Fox was president of Mexico from 2000 to 2006 and is currently co-president of the Centrist Democrat International, an international organisation of Christian democratic political parties.

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Mr Trump quickly hit back on Twitter, attacking the language used and demanding an apology.

He has been promising to build a wall on the southern US border with Mexico since July 2015, as part of an immigration platform that includes deporting undocumented workers.

The policy attracted new media attention last week when the Pope singled it out for criticism during a visit to Mexico.

“Anyone, whoever he is, who only wants to build walls and not bridges is not a Christian,” the pontiff said during a stadium appearance.

Mr Trump then became the subject of a Games of Thrones video mashup by Insiders editor Huw Parkinson.

‘Democracy cannot take crazy people’

Asked whether he was afraid that the front-runner for the Republican nomination could be the next US president, Mr Fox said: “Not at all. Democracy cannot take crazy people that doesn’t know what’s going on in the world today.”

But Mr Fox admitted he was worried about the fact Mr Trump won the backing of 46 per cent of Hispanics who voted in the Republican caucus in the western state of Nevada.

“I’d like to know who those Hispanics are because they again, they’re followers of a false prophet,” he said.

“Please, you Hispanics, Latinos in the US, open your eyes. It’s not to defend our race. It’s not to defend our creed. It’s to defend this very same nation that is hosting you,” he said, referring to the United States.

“This nation is going to fail if it goes into the hands of a crazy guy.”

Another former Mexican president, Felipe Calderon, also lashed out at Mr Trump’s wall idea this month.

“Mexican people, we are not going to pay any single cent for such a stupid wall. And it’s going to be completely useless,” Mr Calderon, who was president from 2006-2012, told CNBC.

“The first loser of such a policy would be the United States.”

Mr Trump has angered Mexico by saying the country was sending rapists across the border and vowed to make the country pay for a wall if he is elected.

President Enrique Pena Nieto’s administration has called those comments “prejudiced and absurd.”

During a visit to Mexico City on Thursday, US Vice President Joe Biden told Mexican officials the rhetoric by Republican candidates against Mexicans was “dangerous” and “disturbing” and did not reflect the views of the vast majority of Americans.