Donald Trump has vowed to deport millions of people in his "first hour" of office if he becomes president at the end of a day in which he stoked tensions with Mexico over the issue of immigration and who would pay for a border wall.
Seeking to end confusion over his aggressive but muddled language on immigration, he vowed to remove those living in the country illegally if he becomes president, warning that failure to do so would jeopardise the "well-being of the American people."
He also vowed to create a special "deportation force" that would seek to remove all who didn't have permission to live and work in the country.
"Anyone who has entered the United States illegally is subject to deportation. We will begin moving them out, day one. My first hour in office, those people are gone.”
He added: "There will be no amnesty."
He also told the crowd that he would introduce "extreme vetting" of immigrants.
Mr Trump was speaking in Phoenix hours after his controversial trip to Mexico in which the billionaire businessman met Mexican President Enrique Peña Nieto over the building of a border wall between the two countries.
The two had held a private meeting on Wednesday afternoon, followed by a joint press conference where Mr Trump said the issue of a border wall did come up but that they did not talk about who would foot the bill.
But Mr Nieto later contradicted the Republican candidate, and said that he “made it clear” that Mexico will not pay for the wall the New York tycoon wants to build.
“At the beginning of the conversation with Donald Trump,” the Mexican president tweeted. “I made it clear that Mexico will not pay for the wall.
Mr Nieto, speaking on TV shortly after, went on the offensive still further, saying Trump posed a threat to his country: "His policy stances could represent a huge threat to Mexico, and I am not prepared to keep my arms crossed and do nothing," he said.
"That risk, that threat, must be confronted. I told him that is not the way to build a mutually beneficial relationship for both nations."
And relations between the pair plunged even further when Mr Trump, just hours later, rowed back on his seemingly conciliatory tone earlier by insisting "100%" that Mexico would pay for the wall.
The Hillary Clinton campaign bashed Donald Trump’s last-minute visit to Mexico, and said “he got beat in the room and lied about it”.
“Donald Trump has made his outlandish policy of forcing Mexico to pay for his giant wall the centrepiece of his campaign,” said Hillary for America chair John Podesta. “But at the first opportunity to make good on his offensive campaign promises, Trump choked.”
He continued: “What we saw today from a man who claims to be the ultimate ‘deal maker’ is that he doesn’t have the courage to advocate for his campaign promises when he’s not in front of a friendly crowd. We know who he is.”
Prior to the appearance, Ms Clinton took aim at Mr Trump for his “dropping in” on Mexico.
“You don’t build a coalition by insulting our friends or acting like a loose cannon. You do it by putting in the slow, hard work of building relationships,” the former Secretary of State said at an event in Cincinnati.
“It’s more than a photo op,” she added. “And it certainly takes more than trying to make up for a year of insults and insinuations by dropping in on our neighbours a few hours and then flying home again. That is not how it works.”