Republican presidential candidate Donald Trump - fresh from a controversial visit to Mexico - reaffirmed his pledge to build a wall on the southern border, make Mexico pay for it, and to start a massive deportation drive from his first day in office.

Just hours after returning from a visit to Mexico City - where the wall was an especially contentious issue - Mr Trump pointedly made it the first issue in his 10-point plan on immigration.

"We will build a great wall along the southern border. And Mexico will pay for the wall. 100 per cent. They don't know it yet, but they're going to pay for it," he said as the crowd launched into chants of "build that wall". The speech, in which the tycoon returned to many of the hawkish themes that have resonated with his fan base, effectively shut down any talk that he was softening his approach to broaden his appeal. And while most of the ideas in his plan were reaffirmations of promises already made, Mr Trump also laid out some new details.

He did not repeat his proposal for a temporary ban on Muslims entering the country but instead promised not to issue visas to people coming from parts of the world where "adequate screening cannot occur". He named Syria and Libya as two such places.

Perhaps the most surprising proposal was what appeared to be a new standard for immigrants, based on "merit, skill and proficiency" - a test that critics said would have excluded many of the labourers who were early immigrants to the United States.

Speaking at the rally on Wednesday, Mr Trump said: "We take anybody. Come on in, anybody. Just come on in. Not any more... Remember, under a Trump administration, it's called America first. Remember that. To choose immigrants based on merit. Merit, skill and proficiency. Doesn't that sound nice?"

Yet, aspects of his plan continued to confuse. Much of the uncertainty in the week leading up to the speech centred on how Mr Trump intended to deal with millions of undocumented immigrants who had not engaged in criminal activity.

Mr Trump had earlier vacillated between working with them to let them stay and saying all of them would have to be deported. In Arizona, he expressed both positions.

He said: "There will be no amnesty. Our message to the world will be this: You cannot obtain legal status or become a citizen of the United States by illegally entering our country."

Yet, in the next breath, he appeared to be open to reconsidering their fates, once his other immigration reforms were in place.

"Importantly, in several years, when we have accomplished all of our enforcement and deportation goals and truly ended illegal immigration for good... then, and only then, will we be in a position to consider the appropriate disposition of those individuals who remain," he said.

Pundits said the speech could be seen as an attempt by Mr Trump to shore up his base, instead of an attempt to broaden it. In that sense, it seemed to work at odds with the motives behind his visit to Mexico.

His foray into a country where his approval rating is 2 per cent was seen as a bold, if risky, attempt to improve his image among Hispanic voters, and to prove he has the temperament to represent the US on the world stage.

And for much of the day, he appeared to be sticking to the plan.

Mr Trump put on his most restrained, presidential public appearance during a joint press conference with Mexican President Enrique Pena Nieto.

While he stood firm on his differences with the Mexican leader on free trade, Mr Trump was respectful and even complimentary to his hosts.

Reading from a prepared script, he said Mexican-Americans were "beyond reproach" and "spectacular, hardworking people". He even called Mr Nieto - who had previously compared Mr Trump to Adolf Hitler and Benito Mussolini - a friend.

Then, when asked about his proposal to make Mexico pay for his border wall, he said the issue of payment was not discussed.

That would later become a point of contention. Though Mr Nieto did not challenge Mr Trump when he was standing beside him, the embattled Mexican leader later directly contradicted the tycoon by tweeting that he had made it clear Mexico would not pay for the wall.

The campaign of his rival, Democratic nominee Hillary Clinton, quickly jumped on the incident, saying Mr Trump "choked" by not bringing up his core campaign promise with Mr Nieto.

Clinton campaign chairman John Podesta said: "It turns out Trump didn't just choke, he got beat in the room and lied about it."