The pontiff said Trump's views on U.S. immigration as "not Christian" in a sign of growing international concern at the billionaire businessman's election prospects.

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Trump has fired back at this accusation. According to CNN, Trump released a statement, saying;

“No leader, especially a religious leader, should have the right to question another man’s religion or faith,” he said in statement. Trump added that the government in Mexico, where Francis spent the past five days, has “made many disparaging remarks about me to the Pope.”

“If and when the Vatican is attacked by ISIS, which as everyone knows is ISIS’s ultimate trophy, I can promise you that the Pope would have only wished and prayed that Donald Trump would have been president,” Trump said.

Later, Trump admitted he regrets his outburst.

“I don’t like fighting with the Pope,” Trump said at a GOP town hall debate in South Carolina hosted by CNN. “I like his personality; I like what he represents.”

Trump further said the Pope is a pawn of the Mexican government, but the Pope made light of his claims.

Before the Pope left for Mexico, Trump called Francis “a very political person” and suggested that the pontiff, who celebrated Mass Wednesday near the U.S.-Mexican border, was a pawn of the Mexican government.

The Pope made light of Trump’s accusations.

"Thank God he said I was a politician because Aristotle defined the human person as ‘animal politicus.’ So at least I am a human person,” he said. “As to whether I am a pawn, well, maybe, I don’t know. I’ll leave that up to your judgment and that of the people.”