(CNN) – Pope Francis spoke of his “sadness, indignation and shame” over the Catholic Church’s role in the abuse of Native Canadian children in boarding schools, as he began a week-long “repentant pilgrimage” to the country.

The Pope apologized and promised a “serious investigation” into what happened in a speech at a meeting with indigenous people in Edmonton, Alberta, on Monday.

Indigenous leaders have long demanded a papal apology for the damage done over the decades to Aboriginal children, who have suffered abuse and the erasure of Aboriginal culture in the country’s boarding schools.

“I apologize, in particular, for the way in which many members of the Church and religious communities cooperated, particularly through their indifference, in the projects of cultural destruction and forced assimilation promoted by governments at the time, culminating in the boarding school system,” the Pope said.

Last year, hundreds of unmarked graves were discovered on the grounds of former residential schools in British Columbia and Saskatchewan.

The Canadian Truth and Reconciliation Commission reported that more than 4,000 Aboriginal children died of neglect or abuse in boarding schools, many of which were run by the Catholic Church.

“In the face of this unfortunate evil, the Church kneels before God and asks him to forgive the sins of his children,” Pope Francis said. “I humbly ask forgiveness for the evil committed by many Christians against indigenous peoples.”

The Pope stressed that his apology is only the first step in correcting these errors.

“An important part of this process will be doing serious fact-finding about what happened in the past and helping boarding school survivors experience recovery from the trauma they have experienced,” he said.

Pope Francis will also travel to Quebec and Iqaluit, the capital of the Canadian territory of Nunavut, during the trip. He will be accompanied during his visit by two Canadian cardinals, Cardinal Mark Ole and Cardinal Michael Czerny.

Francisco, 85, canceled a trip to Africa earlier this month due to knee problems.

With information from Rob Pechetta on CNN, Livia Burgess, and Cecilia Armstrong