The file photo shows the Marieval Indian Residential School in Canada.

Hundreds of unmarked graves, many believed to be of children, have been found at the site of another former Church-run residential school in Canada.

The graves are located near the former Marieval Indian Residential School in Saskatchewan, said the Federation of Sovereign Indigenous First Nations (FSIN), which represents 74 nations in the province, in a press release on Wednesday.

The federation did not give a specific number but said, The number of unmarked graves will be the most significantly substantial to date in Canada.

Cowessess First Nation Chief Cadmus Delorme is expected to reveal details of the horrific and shocking discovery during a press conference on Thursday morning, as well as the latest count of newly-identified remains.

The development comes a month after a mass grave containing the remains of 215 children was discovered at the Kamloops Indian Residential School in British Columbia, which reopened old wounds among the indigenous population in Canada.

At the time, experts warned that the discovery was likely only the beginning.

According to a source with knowledge of the discovery, the total number of graves found near Marieval is expected to be over three times higher than the 215 discovered recently in Kamloops.

The latest findings came after a First Nation teamed up with an underground radar detection team from Saskatchewan Polytechnic to begin the search just over three weeks ago.

Delorme told the Leader-Post in an interview in late May that he did not know how many people’s remains might be discovered. It is estimated that only one third of the graves are marked.

The pain is real, the pain is there, and the pain hasn’t gone away. As we heal, every Cowessess citizen has a family member in that gravesite. To know there’s some unmarked, it continues the pain, Delorme said, adding that the goal was to identify, to mark and to build a monument in honoring and recognizing the bodies that lay (there).

The Marieval Indian Residential School was founded and operated by the Roman Catholic Church from 1899 to 1997 and was located about 165 kilometers east of Regina. The administration of the school was handed over to the federal government in 1969 and then to the Cowessess First Nation in 1987 before it was closed in 1997.

According to Canada’s National Center for Truth and Reconciliation records, everything but the church, rectory, and cemetery was demolished shortly after.

James Daschuk, a University of Regina health and Indigenous history researcher, applauded Delorme’s decision to pursue these searches despite the horrific findings likely to emerge.

As terrible, and I mean absolutely freaking terrible, as this is, what we’re seeing is the community taking their story back, Daschuk said in an interview on Wednesday.

I think this is going to be a pretty important time for healing for the affected communities. But this should also be a serious time for reflection and then action on that reflection for all Canadians, he added.

Canada’s Truth and Reconciliation Commission (TRC)’s report in 2015 determined that at least 3,200 Indigenous children died while attending residential schools, and that the general practice was not to send the bodies of students who died at schools to their home communities.

Canada’s residential school system forcibly separated more than 150,000 First Nations children from their families between 1831 and 1996. Many of the children separated from their homes by the church’s school system were subjected to abuse, rape, and malnutrition. In 2008, the Canadian government formally apologized.