CALGARY, Alberta — The remains of as many as 751 people, mainly Indigenous children, were discovered at the site of a former school in the province of Saskatchewan, a Canadian Indigenous group said Thursday.

The discovery, the largest one to date, came weeks after the remains of 215 children were found in unmarked graves on the grounds of another former boarding school in British Columbia.

Both schools were part of a system that took Indigenous children in the country from their families over a period of about 113 years, sometimes by force, and housed them in church-run boarding schools, where they were prohibited from speaking their languages.

Many children never returned home and their families were given only vague explanations of their fates, or none at all. Canada had about 150 residential schools and an estimated 150,000 Indigenous children passed through the schools between their opening, around 1883, and their closing in 1996.

“This was a crime against humanity, an assault on a First Nation people,” Chief Bobby Cameron, of the Federation of Sovereign Indigenous Nations, the provincial federation of Indigenous groups, said Thursday. “The only crime we ever committed as children was being born Indigenous.”

It is unclear how the children died at the schools, which were buffeted by disease outbreaks a century ago, and where children faced sexual, physical and emotional abuse and violence. Some former students of the schools have described the bodies of infants born to girls impregnated by priests and monks being incinerated.

The National Truth and Reconciliation Commission estimated that about 4,100 children went missing nationwide from the schools. But an Indigenous former judge who led the commission, Murray Sinclair, said this month that he now believed the number was “well beyond 10,000.”

The discovery in Saskatchewan was made by the Cowessess First Nation at the Marieval Indian Residential School, about 87 miles from the provincial capital, Regina.

Local Indigenous leaders on Thursday demanded an inquiry into what they called a “genocide,” and called for the church and the government to turn over all records related to the administration of the schools.

Chief Cadmus Delorme, of the Cowessess First Nation, also called for Pope Francis to apologize, saying that the Roman Catholic Church needed to address its actions.

Delorme said that his Indigenous community, spurred by the discovery at Kamloops and in conjunction with technical teams from Saskatchewan Polytechnic, began combing the area using ground penetrating radar on June 2, hitting as many as 751 unmarked graves. He said he expected more bodies would be discovered.

Canada’s 1.7 million Indigenous citizens make up about 4.9% of the population.