Donald Trump has hit back at the Pope, calling him “disgraceful” over remarks he made about the presidential hopeful’s views on immigration.
Pope Francis had said the Republican candidate was “not Christian” over his apparent wish to build a wall between the US and Mexico.
“A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian,” he said.
While the Pope 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 quickly.
“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.”
However, Mr Trump later appeared to soften his stance, saying during a town hall event that he now believes the Pope’s remarks were “probably a little bit nicer” than first reported.
He said he believes that Pope Francis had heard only one side of the story, as told by the Mexican government, and was not aware of the problems Mr Trump claims are caused by a porous border.
Mr Trump also said he had great respect for the Pope but pointed out: “He’s got an awfully big wall at the Vatican.”
Mr Trump has promised throughout his campaign to build a wall along the US-Mexico border and to deport some 11 million immigrants living illegally in the US.
He has also proposed a temporary ban on Muslims entering America.
The Pontiff capped his five-day trip to Mexico by praying at the country’s border for people who died trying to reach the US.
His comments on Thursday came amid a freewheeling conversation with reporters, during which he also addressed a potential softening of the Church’s ban on contraception because of the Zika virus.