The Sisters of Bon Secours nuns in charge of Mother and Baby Home in Tuam, Co Galway, where the burial of hundreds of babies in a septic tank mass grave has been uncovered have said they no longer hold the burial records.
The nuns, which operated the home said they were shocked and deeply saddened by reports of the burial of 798 dead infants from 1925 to 1961.
It was one of 10 similar homes across Ireland - three others which have little angels plots are believed to hold the remains of another 3,200 babies and infants.
Archbishop of Dublin Diarmuid Martin has called for the religious orders which ran these institutes to release full details of all the people they took in.
In a statement, Bons Secours said it handed its records to the state after it closed its doors.
"In 1961 the home was closed. All records were returned to the local authority, and would now be within the Health Service Executive, Co Galway," the order said.
The nuns said they are committed to engaging with Catherine Corless, the historian who identified the extent of the burials, and the Tuam graveyard committee, which is seeking a permanent memorial at the site.
The order also said it welcomes the Government review of records of what happened in Tuam.
Locally it had been suggested that the burial site could date back to famine times after it was uncovered by two youngsters in 1975.
But amid growing national and international disgust at the details from the town, the Archbishop said the practice of the mass burials was sickening.
"The Gospel message is that authentic faith is measured by how we treat children who represent Jesus Christ," he said.
"Every effort should be made, by all parties who were involved in setting up, running and overseeing these homes, to ensure the mothers and children who were sent there have an accurate account as possible of their own life stories."
All that remains of the site in the town is a grassy area on the edge of a housing estate near where the home stood and where the concrete septic tank is understood to lie.
And the story has earned a renewed focus after campaigners pressed the nuns and the local diocese for a permanent memorial with the name of every child engraved on it.
It has also prompted claims that the site should be declared a crime scene.
The Republic's Children's Minister Charlie Flanagan said the alleged practice in Tuam is almost almost too graphic and horrible to believe.
"It is fully recognised by me and my Government colleagues that we need to establish the truth," he said.
The Irish government review of mother and baby homes will not be restricted to Tuam and includes officials in departments of children, justice, health, education and environment.
"The government is committed to ensuring that the most appropriate action is taken to ensure that the concerns in regards to these deeply tragic and disturbing past events can be addressed," Mr Flanagan said.
The minister also said mother and baby homes were not unique to Ireland, nor was the manner in which the country dealt with its most vulnerable citizens entirely unique.
He said the practice in the 20th century reflects a brutally, unforgiving response by society, religious and state institutions and, in many cases, families to young women and children when they were in most need and most vulnerable.
Other mother and baby homes with little angel's plots include three run by the Sacred Heart Sisters at Sean Ross Abbey, Tipperary - where the story of Philomena Lee began - Bessborough, Co Cork, and Castlepollard, Co Westmeath.
The records of the deaths - even if the birth had not been registered - were kept in ledgers under the 1934 Maternity Act and are now held by the state in private record offices in Galway, Waterford, Cork and Donegal.
About 35,000 single women are believed to have spent time in one of 10 homes for pregnant women.
Another home where the scandal of unmarked graves was uncovered is the Protestant Bethany Home in Dublin, which was found to have had 222 infants die before being secretly buried.
They have since been re-interred and a memorial placed on the new plot in Mount Jerome Cemetery, Harold's Cross.
A spokesman for the Bethany Survivors Group said: "It is imperative that the Government takes action to face up to this shocking episode in the history of the State.
"The issue is gathering a momentum and becoming unstoppable.
"Bethany Home Survivors support the current inquiry call and renew the demand for redress and compensation, for survivors of all so-called mother and baby homes."
The mother and baby homes were excluded from a redress scheme in 2005.
Archbishop Martin said he hopes a full bodied inquiry will be set up to examine all aspects of life in the homes and also how adoptions were organised.
He said the story of the homes was not one from another time or era but the personal story of hundreds of men and women alive today, living in Ireland and abroad.
Archbishop Martin said he had ordered an audit of diocesan files connected to mother and baby homes several months ago.
Hundreds of documents have been collated and will be made given to any public inquiry that is set up but no information of mass graves has emerged.
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'Priest said Mass, then grave was covered up again'
The person who discovered the remains of hundreds of babies in a septic tank has recalled the "tiny skeletons" he encountered when he unearthed the grave when he was just 12 years old.
Frannie Hopkins was playing with a friend at the site back in 1975 when the pair noticed that one of the slabs covering an old septic tank had come loose.
"At the time we found a concrete slab over what I described at the time as a tank, I now see it was a tomb," he said.
"We removed the lid and we found that it was full of skeletons; they appeared to be that of children. They were tiny skeletons, there just seemed to be an awful lot for one small little grave.
"A few days later, our parents told us not to go there, that the priest had been there and had said Mass and prayers and that the grave had been covered up again."
Mr Hopkins said he visited the grave site repeatedly over the years, but never knew the true extent of the tragedy until Catherine Corless's research emerged.
Meanwhile, locals who lived near the site paid special tribute to local man Padraic Dooley, who cared for the tiny graveyard for 40 years. Sadly, Mr Dooley passed away just two weeks ago before the gravesite could be properly recognised.
"Padraic looked after it for more than 30 years. He would always keep flowers there. It's a pity he can't see this now.
"We would have Masses and special blessings at the grave over the years. We knew there were some babies buried here but we never knew how many," said one local man.
Now locals are eager for the site to be marked but insist that they want to see the babies left undisturbed.
As calls for a government inquiry grow, Minister for Children Charlie Flanagan accepted that the Tuam mother-and-baby home was not unique in Ireland, adding: "We will properly review these issues and we will not confine this review to Tuam."
Minister for Public Expenditure and Reform Brendan Howlin said all necessary inquiries would take place, including a criminal one if it was deemed appropriate by the authorities.
A statement on behalf of the Sisters of Bon Secours said they were "shocked and deeply saddened" by the recent reports about St Mary's Mother-and-Baby Home.
"The Bon Secours Sisters say they are committed to engaging with Catherine Corless, the Graveyard Committee and the local residents as constructively as they can on the graves initiative connected with the site.
"The Sisters welcome the recent government announcement to initiate an investigation, in an effort to establish the full truth of what happened," it added.
Earlier, the Archbishop of Dublin Diarmuid Martin urged those responsible for running any of the mother-and-baby homes in Ireland, or people with information about mass graves, to go to the authorities.
He called for a "full-bodied inquiry" to be set up and revealed that he had tasked the Dublin diocesan archivist to compile all information concerning the mother-and-baby homes in Dublin. This information will be passed on to any government inquiry.
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