Donald Trump

He told a cheering crowd in Arizona that he would secure the border, and left open the possibility that millions of illegal immigrants be deported.

Hours earlier, he met the Mexican President Pena Nieto but said they did not discuss who would pay for the wall.

The president later insisted he had told Mr Trump Mexico would not pay.

There had been speculation that the Republican candidate would back off his plan to deport the estimated 11m undocumented immigrants living in the US.

It meanders through two of the most hotly contested battleground states, both prime targets for Donald Trump and Hillary Clinton.

Ohio, the classic bellwether, has picked the winner in every presidential election since 1960. Pennsylvania has voted Democrat in the past six contests, but Donald Trump has designs on turning this reliably blue state Republican red.

Mr Trump said he did not discuss who would pay for the wall.

He also called Mexicans "amazing" and "spectacular" people, in contrast to earlier comments branding Mexican migrants "rapists" and "murderers".

Mr Pena Nieto said Mexicans had been hurt but he respected that Mr Trump genuinely wanted to build relations.

Mr Trump will later fly to Phoenix, Arizona, to deliver a key speech on measures to tackle illegal immigration.

The Republican has seen his poll ratings slip since the party conventions last month.

"I have accepted the invitation of President Enrique Pena Nieto, of Mexico, and look very much forward to meeting him tomorrow," Trump tweeted as reports swirled that Trump was mulling a last-minute trip to Mexico.

The office of the Mexican President confirmed in a tweet late Tuesday night that Trump had accepted Peña Nieto's invitation and that the two will meet privately on Wednesday.

The Republican presidential nominee weighed in on the San Francisco 49er's decision to sit during The Star-Spangled Banner in a pre-game ceremony.

Mr Kaepernick said he will continue to sit out the national anthem until he sees improvements in US race relations.

Mr Trump called the quarterback's controversial stand a "terrible thing."

"I think it's a terrible thing, and you know, maybe he should find a country that works better for him," Mr Trump told KIRO radio in Seattle. "Let him try. It won't happen."

Facing headwinds among moderate voters who view his past rhetoric as racist, but trying to assuage his core conservative base, Trump has attempted something of an image makeover during the past two weeks -- leaving Democrats and Republicans alike unclear on where actually Trump stands.

"I will be making a major speech on ILLEGAL IMMIGRATION on Wednesday in the GREAT State of Arizona. Big crowds, looking for a larger venue," Trump's tweet said.

Trump's immigration policy received renewed scrutiny recently after he seemingly softened his stance on how to treat undocumented immigrants and then reaffirmed his support for deporting them. He's been consistent on a few points, however: building a US-Mexico border wall, "extreme vetting" of new immigrants and deportations of those who commit crimes.

The Republican nominee retweeted a supporter's post that the Democratic nominee "said a KKK member was her mentor." And speaking later in Des Moines, Iowa, he dredged up Clinton's use of the term "super predators" in the 1990s to argue that he, not Clinton, offered African-Americans the best choice for president.

Speaking on the campaign trail in Iowa, he outlined what he called an "entry-exit" programme, which would track those who overstay their visas.

He also reiterated his support for building a wall along the southern border with Mexico.

And he said he would stop illegal immigrants getting welfare benefits.

"I am going to build a great border wall, institute nationwide e-verify, stop illegal immigrants from accessing welfare and entitlements, and develop an exit-entry tracking system to ensure those who overstay their visas are quickly removed," Mr Trump said.

Harold Bornstein, Trump's doctor who wrote a four-paragraph note last December declaring the GOP nominee to be the "healthiest individual ever elected to the presidency," said Friday that he spent very little time on the note.