Pope Francis
Pope FrancisReuters

U.S. presidential candidate Donald Trump did not spare even Pope Francis from his barbs, after the latter questioned his "Christianity." 

Coming down hard on Trump's views on immigrations, Pope Francis said Thursday that "a person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian," according to Reuters. The Roman Catholic Church's leader made his point with reference to Trump's plan of building a wall along the U.S. border with Mexico.

Trump called the Pope's comments about his faith "disgraceful", and also suggested that only he could stop the Islamic State group from attacking the Vatican. 

"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," Trump said in a statement on social media. 

He also said that Pope Francis had heard only "one side of the story" and accused the Mexican government of making "disparaging" remarks about him and of "using the Pope as a pawn."

"For a religious leader to question a person's faith is disgraceful. I am proud to be a Christian and as President I will not allow Christianity to be consistently attacked and weakened, unlike what is happening now, with our current President," Trump said. 

"No leader, especially a religious leader, should have the right to question another man's religion or faith. They are using the Pope as a pawn and they should be ashamed of themselves for doing so, especially when so many lives are involved and when illegal immigration is so rampant."

The Pope was on a five-day trip to Mexico and returned to Rome, Thursday. 

He was also reportedly asked by reporters during an in-flight conference whether American Catholics should vote for Trump in the US Presidential election, but he said he would not get involved in that.

"As far as what you said about whether I would advise to vote or not to vote, I am not going to get involved in that. I say only that this man is not Christian if he has said things like that. We must see if he said things in that way and in this I give the benefit of the doubt," Pope Francis said.