More than 750 unmarked graves have been found near a former Catholic boarding school for indigenous children in western Canada, a tribal leader said Thursday -- the second such shock discovery in less than a month.

The revelation once again cast a spotlight on a dark chapter in Canada's history, and revived calls on the Pope and the Church to apologize for the abuse suffered at the schools, where students were forcibly assimilated into the country's dominant culture.

"As of yesterday, we have hit 751 unmarked graves" at the former Marieval boarding school in Saskatchewan province, Cowessess First Nation Chief Cadmus Delorme told reporters.

"This is not a mass grave site. These are unmarked graves," he said, adding that each plot would be assessed in the coming weeks to determine the number of victims buried at the site.

Delorme said the graves -- found through ground-penetrating radar mapping -- may at one time have been marked, but "Catholic Church representatives removed these headstones," adding that doing so is a crime in Canada and they were treating the site "as a crime scene."

"Without a doubt, they were trying to cover up the amount of children that were being mistreated and killed in those institutions," Bobby Cameron, head of the Federation of Sovereign Indigenous Nations in Saskatchewan, told broadcaster CBC.

"We had concentration camps here," Cameron said separately at a news conference. "Canada will be known as the nation who tried to exterminate the First Nations."

A new discovery of hundreds of unmarked graves near a former school for indigenous in western Canada follows the earlier unearthing of children's remains at another school in Kamloops, British Columbia
A new discovery of hundreds of unmarked graves near a former school for indigenous in western Canada follows the earlier unearthing of children's remains at another school in Kamloops, British Columbia AFP / Cole Burston

The exact number of victims will not be known for weeks because the radar mapping equipment has a margin of error and graves may contain more than one set of remains, said Delorme.

Excavations at the Marieval school, about 150 kilometers (90 miles) east of the provincial capital Regina, began at the end of May, after the discovery of the remains of 215 schoolchildren at another such former school in British Columbia.

That first find at the Kamloops school triggered excavation work near several former institutions for indigenous children across Canada, with the assistance of government authorities.

Until the 1990s, some 150,000 Native American, Metis and Inuit children were forcibly recruited into 139 of these residential schools across Canada, where they were isolated from their families, language and culture.

Many were subjected to ill-treatment and sexual abuse, and more than 4,000 died in the schools, according to a commission of inquiry that concluded Canada had committed "cultural genocide."

Cameron described the finding as "a crime against humanity."

"The only crime we ever committed as children was being born indigenous," he said.

Prime Minister Justin Trudeau called the findings at both Kamloops and Marieval "a shameful reminder of the systemic racism, discrimination and injustice that indigenous peoples have faced -- and continue to face -- in this country."

The discovery of unmarked graves at a former residential school for indigenous children in Canada's Saskatchewan province follows a similar relevation in British Columbia
The discovery of unmarked graves at a former residential school for indigenous children in Canada's Saskatchewan province follows a similar relevation in British Columbia AFP / Cole Burston

"Together, we must acknowledge this truth, learn from our past and walk the shared path of reconciliation, so we can build a better future," he said.

The Marieval residential school in eastern Saskatchewan hosted indigenous children until the mid-1990s before being demolished and replaced by a day school.

One former student, Barry Kennedy, told CBC he was shocked by the news but not surprised.

"During my time at Marieval Indian Residential School, I had a young friend that was dragged off one night screaming," he said, adding that he never saw the child again.

"His name was Bryan... I want to know where Bryan is," Kennedy said.

He described a history of violence at the school.

"We were introduced to rape. We were introduced to violent beatings. We were introduced to things that weren't normal with our families," he added.

And he said he imagined the graves found so far were just the tip of the iceberg: "By the stories that... were told by our friends and fellow students, there are multiple locations, you know, per school."

Searches have already turned up possible unmarked burial sites in Ontario and Manitoba provinces.

"We will find more bodies and we will not stop till we find all of our children," Cameron said at the press conference.

Added Delorme: "We all must put down our ignorance and accidental racism at not addressing the truth that this country has with indigenous people."

"This country must stand by us."

In early June, a few days after the discovery of the bones in Kamloops, UN human rights experts urged Ottawa and the Vatican to conduct a full and prompt investigation.