Pope Francis has intervened explosively in the US election campaign, saying Donald Trump cannot claim to be a Christian while vowing to build a border wall to keep out immigrants.
“Anyone, whoever he is, who only wants to build walls and not bridges is not a Christian,” the pontiff told journalists during his return journey from a trip to Mexico.
He was responding to a question about the Republican White House hopeful’s anti-immigrant stance.
“Vote, don’t vote, I won’t meddle. But I simply say, if he says these things, this man is not a Christian,” Pope Francis said.
“We need to see if he really said them and for this I will give him the benefit of the doubt.”
Despite that qualifier, Pope Francis’s remarks drew swift and angry condemnation from the billionaire tycoon.
“For a religious leader to question a person’s faith is disgraceful,” Mr Trump said in a statement delivered on a campaign stop in South Carolina.
“I am proud to be a Christian and as president I will not allow Christianity to be consistently attacked and weakened.”
Mr Trump has gained popularity by claiming Mexico is sending criminals to the United States, and last week he accused the Pope of visiting the border between the two countries at the bidding of the Mexican government.
Pope Francis was speaking after concluding a five-day trip to Mexico, where he delivered a mass before 300,000 people near the US border and decried the “human tragedy” of migrants fleeing violence worldwide.
In a highly symbolic gesture the pontiff climbed a ramp facing the Rio Grande and looked out across the border into US territory, where hundreds of migrants waved at him.
Will Trump v Francis affect the polls?
The absolute media maelstrom around Donald Trump has only gotten that much bigger as they head into the South Carolina primary, where he’s courting the evangelical vote.
There’s a national poll out saying Senator Ted Cruz has passed him but he’s been the frontrunner in the Republican presidential campaign since he began in June last year.
He won in New Hampshire, came second in Iowa, and he’s heading into South Carolina with a 15-20 per cent lead on some people.
If the polls bear out, he’s going to win that, and I don’t think Americans are going to be too upset — at least people that would potentially support Donald Trump — that some guy who lives in Rome and is the leader of the Catholic Church has attacked their guy, their man — their bulwark against the elite, so to speak.
Analysis by North America correspondent Michael Vincent
Mr Trump has vowed to build a wall on the US southern border to keep migrants from illegally crossing into the United States, a pledge that has caused a firestorm in the presidential campaign, where immigration is a hot-button issue.
His reaction to the Pope’s comments was scathing.
“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 because this would not have happened,” Mr Trump said, using an acronym for the militant group.