REGINA, Saskatchewan (AP) — The chief of a Indigenous nation in Canada said Thursday investigators have found 751 unmarked graves at the site of a former residential school for Indigenous children — a discovery that follows last month's report of 215 at another school.

Chief Cadmusn Delmore of the Cowessess First Nation made the announcement at a news conference.

Chief Bobby Cameron of the Federation of Sovereign Indigenous First Nations said he expects more graves will be found on residential school grounds across Canada.

“This was a crime against humanity, an assault on First Nations,” he said.

“We will not stop until we find all the bodies.”

The bodies were discovered at the Marieval Indian Residential School, which operated from 1899 to 1997 where Cowessess is now located, about 87 miles east of Regina, the capital of Saskatchewan.

Delorme said at one time the graves were marked but those who operated the school removed the markers.

“We are treating this as a crime,” he said.

The Cowessess and the Federation of Sovereign Indigenous First Nations, which represents Saskatchewan’s First Nations, said a day earlier that “the number of unmarked graves will be the most significantly substantial to date in Canada.”

Last month the remains of 215 children, some as young as 3 years old, were found buried on the site of what was once Canada’s largest Indigenous residential school near Kamloops, British Columbia.