Outrage was sparked after a Catholic priest placed an aborted baby on the altar "as a prop" to persuade voters to support Trump.

Father Frank Pavone, head of the controversial pro-life group Priests for Life, posted a video on Facebook on Sunday with him urging voters to back the Republicans with a blood-covered foetus in the foreground.

"Today I am showing him to you because in this election we have to decide if we will allow this child killing to continue in America or not," he wrote.

"Hillary Clinton and the Democratic platform says yes, let the child-killing continue (and you pay for it); Donald Trump and the Republican platform says no, the child should be protected."

Pavone came under fire for the shocking video and Ed Mechmann, director of public policy for the Archdiocese of New York, said it was "absolutely appalling, and deserves to be repudiated by all of us who consider ourselves to be pro-life in the fullest meaning of that word."

In a blog post on the Archdiocese website Mechmann said: "A human being has been sacrificed and the altar of God has been desecrated, all for politics.

"Everyone who respects the dignity of every human person should reject and disavow this atrocity.

"A priest of the Catholic Church publicly displayed on a sacred altar a dead baby who was the victim of a terrible crime as part of a propaganda video in favour of a political candidate," he said. "It is hard for me to express in calm, measured terms, the revulsion I feel about this."

Pavone advocates use of graphic images of aborted foetuses to shock viewers. "America will not reject abortion until America sees abortion," is his slogan. But Mechmann said this was "beside the point".

He wrote: "The real question is, what about that baby as a human being? That baby is an individual human person, someone's son or daughter, made in the image and likeness of God, unique and unrepeatable, and deserving of our love and mercy," he said. "To use her body in this way is to treat that poor lost girl or boy as an object to be used – which is the antithesis of love – and not as a brother or sister to be mourned."

Fr Thomas Petri, vice president and academic dean of the Pontifical Faculty of the Immaculate Conception in Washington, DC, said the "issue here is the dignity of the child that was used, and violating the dignity of his or her body on an altar of God – which is supposed to be used for divine worship".

"It really is a profane violation. The Catholic Church is very strict that human bodies are to be treated reverently after a person dies," he told Catholic News Agency.

As well fellow priests Catholic bloggers reacted with horror at Pavone's video.

"Human bodies are not objects for us to exploit. As we do to them, we do to Christ," Mary Pezzulo wrote on Patheos. Another, Scott Eric Alt, called for Pavone to have his right to celebrate Mass removed. "An altar, whether fixed or movable, is to be reserved for divine worship alone, to the exclusion of any secular usage.

"The altar is intended for a sacramental purpose, as the place where the priest celebrates Mass," Alt said.

"There is no other way to put it than that this is a sacrilege and a scandal. The human person is not a prop for a political stunt. This is an offense to the purpose for which priests are ordained to use the altar."

White Catholics backed Donald Trump by 56 to 31 per cent at the start of October. But the video released showing the Republican candidate making lewd sexual advances as well as allegations of assault have swung the poll in Clinton's favour. Now Catholics overall are polling 61-34 in her favour.