The popularity of Donald Trump among church-going Catholic Republicans has risen since Pope Francis called into question his faith.

A new Ipsos Mori poll has indicated that the proportion of church-going Catholics supporting Trump in the 50 days after the Pope's comments was almost 10 per cent higher than in the 50 days that preceded them.

Pope Francis called into question the Republican frontrunner's faith on February 18 in response to a question about Trump's plans to build a wall on the Mexican border. Francis said: "a person who thinks only of building walls, wherever they may be, rather than building bridges, is not Christian".

A spokesperson for the Vatican later said the Pope was "in no way" singling out Trump, who had branded the comments "disgraceful".

Trump has averaged support among 47.9 per cent of Catholic Republicans since Francis made his remarks, compared to 39.8 per cent previously.

"Many Catholics probably felt that the pope's comments were not a directive on how they should vote or who they should support, and still others may never have been aware of the pope's comments to begin with," Mark Gray, a senior research associate at Georgetown University, told Reuters.

The rise in Catholic Republicans supporting Trump may well have be caused by other factors, including the fall in number of candidates remaining in the race.

However Fr William Paul McKane, a Catholic priest who supports Trump, told Reuters he felt the Pope's comments had damaged his reputation among his followers.

"I call it paradoxical, to put it gently, that the pope said that, when he lives behind walls that are about 40 feet high and 40 feet across. That comment hurt his credibility with my parishoners," he said.

McKane explained that he was voting for Trump because of his clear lines on issues such as security.

"Trump's verbiage does not sound compassionate. I don't hold him up as a paragon of Christian virtue, but I'm not looking for that in a candidate. I'm looking for someone who is prudent and can make good political decisions," he said.

The Reuters/Ipsos poll questioned 1,117 church-going Catholic Republicans.

The Catholic population is a sizeable US voting bloc, making up around one quarter of the electorate, according to Georgetown University's Centre for Applied Research in the Apostolate.