Donald Trump says the Pope is "disgraceful"
Pope Francis thrust himself into the heated American presidential campaign,declaring that Donald Trump is "not Christian" if he wants to address illegal immigration only by building a wall along the US-Mexico border.
Mr Trump hit back ferociously, saying it was "disgraceful" for a religious leader to question a person's faith.
The rare back-and-forth between pontiff and presidential candidate was the latest development in an American election already roiled by Trump's rhetoric and controversial policy proposals, particularly on immigration.
It also underscored the pope's willingness to wade in on controversial issues.
Francis's comments came hours after he concluded a visit to Mexico, where he prayed at the border for people who died trying to reach the US.
While speaking to reporters on the papal plane, he was asked what he thought of Mr Trump's campaign pledge to build a wall along the entire length of the border and expel millions of people in the US illegally.
"A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian," he said. While Francis said he would "give the benefit of the doubt" because he had not heard Mr Trump's border plans independently, he added: "I say only that this man is not a Christian if he has said things like that."
Mr Trump, a Presbyterian and the front-runner for the Republican presidential nomination, responded within minutes.
"For a religious leader to question a person's faith is disgraceful," he said at a campaign stop in South Carolina, which holds a key primary on Saturday. "I am proud to be a Christian, and as president I will not allow Christianity to be consistently attacked and weakened."
Mr Trump also raised the prospect of the Islamic State extremist group attacking the Vatican, saying that if that happened, "the pope would have only wished and prayed that Donald Trump would have been president because this would not have happened".
The billionaire businessman said later that he was "totally respectful" of the pope but stood by his initial response.
Francis, the first pope from Latin America, has been a vocal proponent of compassionate immigration policies.
While Trump's rhetoric has been among the most inflammatory, some of his rivals have staked out similar enforcement positions. Texas Sen Ted Cruz and retired neurosurgeon Ben Carson are among those who have explicitly called for construction of a wall.
Former Florida Gov Jeb Bush, one of the few GOP candidates proposing a path to legal status for people already in the US illegally, said Thursday that he supports "walls and fencing where it's appropriate."
Mr Bush said that while he gets his guidance "as a Catholic" from the pope, he doesn't take his cues from Francis on "economic or environmental policy".
Marco Rubio, another Catholic seeking the GOP nomination, said that Vatican City has a right to control its borders and so does the United States.
Mr Rubio said he has "tremendous respect and admiration" for the pope, but he added, "There's no nation on Earth that's more compassionate on immigration than we are."
Even before Thursday's exchange, Mr Trump had been critical of Francis's visit to Mexico. He said last week that the pope's plans to pray at the border showed he was a political figure being exploited by the Mexican government.
Francis glossed over the assertion that he was a pawn of Mexico, telling reporters on his plane that he would "leave that up to your judgment."