Donald Trump, in a fiery speech on immigration Wednesday, doubled down on his hardline stance, promising to build a "impenetrable, physical, tall, powerful, beautiful" wall across the southern border just hours after meeting with the Mexican president.

In the long-awaited speech in Phoenix, Arizona, amid accusations he was softening his hardline stance on the subject, Trump said that America’s current immigration system “serves the needs of wealthy donors, political activists and powerful politicians.”

“Let me tell you who it does not serve, it does not serve you the American people. It doesn’t serve you,” he said.

In his speech, Trump also promised to end "catch and release," to increase the number of ICE and border patrol agents, block funding for sanctuary cities, create a deportation task force to deport criminal aliens.

He also promised to cancel President Obama's executive actions, and to enforce current immigration laws and  accused Democratic rival Hillary Clinton of not having a plan on immigration, saying she would give "Obamacare, Social Security and Medicare to illegal immigrants, breaking the federal budget."

He told the vibrant crowd that there are some immigrants who will be unable to assimilate into American society.

“It’s our right as a sovereign nation to choose immigrants we think are the likeliest to thrive and flourish and love us,” he said.

He also reiterated his call for a wall along the southern border.

"We will build a great wall along the southern border," he said to cries of "Build that wall" from the boisterous crowd. "And Mexico will pay for the wall."

He later said the wall would be "impenetrable, physical, tall, powerful, beautiful."

Trump’s speech comes after he met with Mexican President Enrique Pena Nieto earlier in the day and asserted America’s “right” to build a border wall during a hastily-arranged visit to Mexico City.

While both leaders adopted a measured and respectful tone, with Trump calling it a "substantive, direct and constructive exchange of ideas," there was disagreement on the question of the wall.

While Trump told reporters “we didn’t discuss payment of the wall,” Pena Nieto later contradicted Trump and said the subject was among those discussed. He also tweeted that he made it clear "that Mexico will not pay for the wall."

Trump has been accused of stoking tensions on the subject ever since he announced his campaign in June of last year in which he accused Mexico of not sending their best people across the border.

“When Mexico sends its people, they’re not sending their best. They’re not sending you. They’re not sending you. They’re sending people that have lots of problems, and they’re bringing those problems with us. They’re bringing drugs. They’re bringing crime. They’re rapists. And some, I assume, are good people,” he said.

In recent weeks, Trump has been accused of softening his tone on the subject, and had been forced to clarify whether he favored a path to citizenship for those here legally, and whether he still planned to build a wall.