A former Mexican president had some tough words when asked about GOP candidate Donald Trump's much-touted plan to build a border wallthat he says will be paid for by Mexico.

"We are not going to pay any single cent for such a stupid wall! And it's going to be completely useless," said former Mexican president Felipe Calderón when asked about this at the AmCham Egypt for Business Conference on Sunday.

Calderón had harsh words about the Republican presidential race during his conversation with CNBC's Hadley Gamble, saying it was "incredible" that quite an "admirable society" like the U.S. had candidates like Trump.

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Former President of Mexico Felipe Calderon speaks on stage during the 2015 Concordia Summit at Grand Hyatt New York on October 1, 2015 in New York City. Leigh Vogel

"No offense, no offense to America. So Donald Trump … is ambitious but not exactly very well-informed man, I don't want to say ignorant, but he is not very well informed," said Calderón.

Trump has made border issues and immigration one of the key centerpieces of his campaign, saying on the day he announced he was running that Mexico was sending "rapists" and "criminals." The controversial remarks set off a cascade of events including strong condemnation from the U.S. Latino community - including Latino Republicans - and the severing of several business relationships including one with NBC. Despite the controversy, Trump has escalated his rhetoric on immigration issues and has called for a ban on Muslims entering the U.S. to combat terrorism.

The former Mexican president said "the first loser of such a policy would be the United States - If this guy pretends that closing the borders to anywhere either for trade [or] for people is going to provide prosperity to the United States, he is completely crazy."

Calderón also took issue with Trump's statements that illegal immigration from Mexico is a big and escalating problem. According to a Pew Research report in November, more Mexicans were emigrating from the U.S. than entering.

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"They don't want to go, they can work for a motor company (that's) not in Detroit, I am sorry to say," said Calderón about the fact that fewer Mexicans want to go to the U.S. "They are working for a motor company in Hermosillo and Toluca, so Mazda is coming to Mexico, Honda is coming to Mexico. Those kids have jobs in that industry in Mexico."

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