Originally Published: 25 JUL 22 13:45 ET

By Jack Guy, CNN

(CNN) -- Pope Francis has spoken of his "sorrow, indignation and shame" over the Catholic Church's role in the abuse of Canadian Indigenous children in residential schools, as he kicked off a weeklong "penitential pilgrimage" to the country.

The Pope apologized and promised a "serious investigation" into what happened in a speech at a meeting with Indigenous peoples in Edmonton, Alberta, on Monday.

Indigenous leaders have long called for a papal apology for the harm inflicted for decades on Indigenous children, who suffered abuse and the erasure of Indigenous culture in the country's residential schools.

"I ask forgiveness, in particular, for the ways in which many members of the Church and of religious communities cooperated, not least through their indifference, in projects of cultural destruction and forced assimilation promoted by the governments of that time, which culminated in the system of residential schools," the pontiff said.

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

And Canada's Truth and Reconciliation Commission has reported that more than 4,000 Indigenous children died either from neglect or abuse in residential schools, many of which were run by the Catholic Church.

"In the face of this deplorable evil, the Church kneels before God and implores his forgiveness for the sins of her children," said the Pope. "I humbly beg forgiveness for the evil committed by so many Christians against the Indigenous peoples."

And the pontiff underlined that his apology is just the first step in righting these wrongs.

"An important part of this process will be to conduct a serious investigation into the facts of what took place in the past and to assist the survivors of the residential schools to experience healing from the traumas they suffered," he said.

The Pope will also travel to Quebec and Iqaluit, capital of the Canadian territory of Nunavut, during the trip. Two Canadian cardinals will accompany him throughout his visit, Cardinal Marc Ouellet and Cardinal Michael Czerny.

Francis, 85, had a trip to Africa earlier this month canceled due to issues with his knee.