Former Mexican President Vicente Fox assured CNN International viewers Tuesday that the border between the United States and Mexico is "very safe," and he claimed there is no problem of terrorist infiltration.

"We have a very safe border," he said.

Fox has been a person of interest in the 2016 presidential election ever since he responded to GOP presidential candidate Donald Trump's oft-repeated promise to build a wall on the southern border and make Mexico pay for it.

"We are not paying, I am not going to pay for that f—king wall. I am not, and he should know that. I am not going to apologize," he said in a separate interview in February.

Trump has responded to these objections by promising to make the wall even taller.

In response, the former Mexican president said in an interview on the Fox Business Network, "My reaction is: More stupid. That's a wrong thought. Migration should be handled in a different manner."

Fox also called on Trump to exit the primary, saying, "I would invite this guy to drop out of the race and go back to his business. He doesn't know a little bit about macroeconomics, he doesn't know about history, he doesn't recognize what [the North American Free Trade Agreement] is about."

"[Mexico is] partially responsible for making that economy as strong as it is," he added.

On Tuesday, Fox continued his criticism of Trump, and maintained again that the billionaire businessman, who alleges terrorists are sneaking into the United States through the southern border, has no idea what he is talking about.

"With really, very carefully issuing visas. Never has a terrorist has come out of Mexico. They came through Canada or just flying in." "So I don't understand [Trump's] confusion," he told CNN International. "He is trying to destroy Mexico."