The Federation of Sovereign Indigenous Nations (FSIN) is demanding an official apology from Pope Francis after the discovery of unmarked graves the band says contain the remains of about 215 children at a former residential school site in B.C.

FSIN Chief Bobby Cameron called for the apology, along with the release of any residential school records the church has not divulged, on Sunday.

"This was genocide, and it should be acknowledged as such by the perpetrators, the church, the government, and the RCMP," wrote Cameron in a statement.

"Survivors and their families deserve an apology for the wrongs committed against them during decades of abuse at federally and church-run residential schools."

The request for a formal apology comes after the Tk'emlúps te Secwépemc First Nation in British Columbia announced the discovery of unmarked burial sites the band says hold the remains of an estimated 215 children on the grounds of the former Kamloops Indian Residential School.

Pope Francis addressed the issue of Canadian residential schools on Saturday, but fell short of a formal apology, saying "May the political and religious authorities of Canada continue to collaborate with determination to shed light on that sad story and humbly commit themselves to a path of reconciliation and healing."

This is not the first time Pope Francis has been invited to Canada to apologize for the Catholic church's role in residential schools. There had been discussions of bringing Pope Francis to Saskatoon's Wanuskewin Heritage Park to make a national apology, but that was officially shut down by the pope in 2018.

Last week, the Regina Archdiocese made an official apology on its website for its role in residential schools, and said that it had a responsibility to 'look anew' at the four residential school sites within its area, all of which contain cemeteries.

"The Archdiocese has a moral obligation to assist in that process, to support the Indigenous communities carrying out that work, and to walk alongside Indigenous brothers and sisters as we face anew the waves of suffering that were part of residential schools," read a statement from Archbishop Donald Bolen.

"In the coming days, we will seek out ways to enter into conversation with these communities while also continuing the dialogue that has already begun with others so that we can offer support and assistance in this work."

The FSIN also called for the release of any residential school records that the Catholic church may have in its possession.

"These institutions must also preserve and release all residential school records, so that true reconciliation and healing can begin and the United Nations can conduct an investigation," read a statement from Cameron.

"Litigation against the release of these records contradicts Canada's claim that their most important relationship is with the First Peoples of these lands. Anything short of this is continued injustice against First Nations people."

Cameron asked all survivors, their families, elders and others to write the Catholic Church, Pope Francis, the RCMP and the federal government asking for the release of all residential schools records so that the United Nations can do an investigation.

Indigenous leaders from across the country are asking for such documents to be released, stating their importance in identifying the remains of any children who may be discovered.

On Friday, Prime Minister Justin Trudeau asked the Catholic Church to hand over any residential school documents it may have in its possession. The religious order that ran the Kamloops school says it is working to digitize and transfer any records it had in its possession.