A right-wing Catholic commentator has dismissed the Tuam mother and baby home atrocity as 'fake news', as the Irish Prime Minister said the home was a 'chamber of horrors'.

Bill Donohue of the Catholic League in New York contradicted bishops as well as politicians by writing that accounts of up to 800 dead babies at the home in County Galway are a 'lie' and a 'hoax'.

'It was a lie in 2014 and it is a lie in 2017,' he said. 'There is no evidence of a mass grave outside a home for unmarried women operated by nuns in Tuam, Ireland, near Galway, in the 20th century. The hoax is now back again, and an obliging media are running with the story as if it were true.'

The comments come as the Irish Taoiseach Enda Kenny said the discovery represented a mass grave and 'a social and cultural sepulchre'.

A state-appointed inquiry has found 'significant human remains' in underground chambers at the site, with tests confirming that the bodies ranged from premature babies to three-year-olds.

The Commission of Investigation is looking into claims, first raised by the local historian Catherine Corless.

The home was one of 10 Irish institutions run by religious orders, to which about 35,000 unmarried pregnant women are thought to have been sent.

A child died there nearly every two weeks between the mid-1920s and 1960s, according to reports.

The home was run by the Bon Secours order of nuns, which has yet to respond to the development.

The Bishop of Limerick, Brendan Leahy, who was representing Catholic Bishops at the Citizens Assembly in Dublin at the weekend, said: 'We're all as shocked about this as everyone else...We hang our heads in shame, but it brings us back to the fact that this is what we want, to promote a culture that really does care for life before and after birth.'

Writing on the Catholic League website, which is not an official Church site, Donohue said: 'The most pernicious aspect of this story is the willingness of the media to be seduced by the most fantastic tales about the Catholic Church, and the profound laziness of reporters to fact check news stories. They are responsible for making this a classic example of fake news.'