Former Mexican President Vicente Fox blasted President Donald Trump on Friday, calling him a "child" and mockingly referring to him as a corporate "CEO" rather than president of the world's most powerful country.

In an interview on CNBC's "Squawk Box," the outspoken Fox said Mexico won't pay for the wall Trump wants to build along the border, "not now, not ever."

Fox also said he doesn't believe Trump is an American "in his soul and his beliefs." He added he does not understand the current state of the United States.

Shortly after Fox's interview, Trump tweeted Friday morning:

Mexico has taken advantage of the U.S. for long enough. Massive trade deficits & little help on the very weak border must change, NOW!

"We get this CEO Trump coming in to sit in the presidential chair and keep acting as a child, as a CEO of his corporations, making deals he says, but he in reality is making mad everybody like it happened with Mexico," Fox said.

"Fortunately, President Pena stood up, faced him and canceled the visit," he said.

Also see: Vicente Fox says US makes mediocre cars and that's why auto industry collapsed

The Mexican peso was relatively stable against the dollar Friday morning, after getting hit Thursday by the Twitter war between Trump and Mexican President Enrique Pena Nieto over the U.S. president's border wall plans. A summit meeting between the two has been canceled.

The White House on Thursday floated the notion of a 20 percent tax on goods from Mexico to pay for the wall.

But later in the day, Trump's press secretary clarified, saying the tax idea was among several under consideration to help fulfill Trump's promise that Mexico would reimburse the U.S. for the cost of building the wall.

Fox said a 20 percent tax on goods from Mexico would actually be a tax on American taxpayers and American businesses because many cars are made in his country.

"Nobody wins on a trade war," Fox said. "This is what we have to make this kid understand, this CEO. It's not the same as business. Trading is a win/win situation. Why he does not speak about Canada? Canada exports more cars to the United States than Mexico. He doesn't say a word there. India is taking away 4½ million jobs from United States on the outsourcing to call centers, software manufacturing in India. And he doesn't say a word."



He said Mexico would have no trouble finding other trading partners.

"We don't worry about trading. We have China to trade with, the second largest world economy," he said. "South America is doing a lot of trading with China. China will come and invest. And I'm sure Senor Trump would not like to see Chinese telecom towers on the border but that's what he's forcing us to do. The world is much, much larger than United States."