He’s called them rapists, illegal immigrants and drug dealers.

He’s promised to build a wall on America’s southern border and make Mexico pay for it.

Now Republican presidential candidate Donald Trump is fronting up – making an unexpected trip to the country he has frequently vilified.

I have accepted the invitation of President Enrique Pena Nieto, of Mexico, and look very much forward to meeting him tomorrow.

— Donald J. Trump (@realDonaldTrump) August 31, 2016

Mr Trump was however mild-mannered on Wednesday, praising Mexicans as “amazing people” following a closed-door meeting at the official residence of the country’s president, Enrique Pena Nieto.

Mr Trump and the Mexican president, who has compared the New York billionaire to Adolf Hitler, addressed reporters from adjacent lecterns before a Mexican flag.

The trip, 10 weeks before America’s presidential Election Day, came just hours before the Republican nominee was to deliver a highly anticipated speech in Arizona about illegal immigration.

That has been a defining issue of his presidential campaign, but also one on which he’s appeared to waver in recent days

With political risks high for both men, Mr Trump stayed on script, declining to repeat his promise to force Mexico to pay for a wall along the border between the two countries when pressed by reporters.

Mexican President Pena Nieto has likened Trump’s tone to that of Hitler. Photo: Getty

“Having a secure border is a sovereign right and mutually beneficial,” he said, reading from prepared remarks.

“We recognise and respect the right of any country to build a physical barrier or wall on any of its borders to stop the illegal movement of people, drugs and weapons.

“Cooperation toward achieving this shared objective – and it will be shared – of safety for all citizens is paramount to both the United States and to Mexico.”

Mr Trump’s presence on Wednesday, his first meeting with a head of state abroad as a presidential candidate, sparked anger and protests across Mexico’s capital city.

A former Mexican president bluntly told the celebrity businessman that, despite Pena Nieto’s hospitality, he was not welcome.

“We don’t like him. We don’t want him. We reject his visit,” former President Vicente Fox told CNN, calling the trip a “political stunt.”

Mr Pena Nieto was less combative as he addressed reporters alongside Mr Trump.

He acknowledged the two men had differences and defended the contribution of Mexicans working in the United States, but he described the conversation as “open and constructive.”

He and Trump shook hands as the session ended.

After saying during his Republican primary campaign he would use a “deportation force” to expel all of the estimated 11 million people living in the United States illegally, Trump suggested last week he could soften that stance.

But he still says he plans to build a huge wall – paid for by Mexico – along the two nations’ border.

He was under pressure to clarify just where he stands in the speech that had been rescheduled several times.

Watch the full speech below.