Pope Francis called his trip to Canada, where he will meet with Indigenous survivors of abuse at Catholic Church-run residential schools, a "penitential pilgrimage" on Sunday.

"Next Sunday, God willing, I will leave for Canada," he said at the end of the Angelus prayer, a clear reference to a knee problem that forced him to cancel a trip to Africa last month.

The pontiff is expected to use his July 24-30 visit to Edmonton, Quebec, and Iqaluit to repeat an apology he delivered to Canadian delegations who visited the Vatican back in April.

The Pope told the crowds gathered in Saint Peter's Square, on Sunday, that he "expressed my sorrow and solidarity for the harm they have suffered."

"And now I am about to make a penitential pilgrimage, which I hope, with God's grace, will contribute to the journey of healing and reconciliation already undertaken," he said.

The visit to Canada is a significant step forward in the Pope’s efforts to address the global scandal of clerical sexual abuse of children and decades of cover-up.

From the late 1800s to the 1990s, approximately 150,000 First Nations, Metis, and Inuit children were enrolled in 139 residential schools across Canada as part of a government policy of forced assimilation.

They were separated from their families, language, and culture for months or years, and many were physically and sexually abused by headmasters and teachers.

More than 1,300 unmarked graves uncovered since last May

It is noteworthy that in late March, Indigenous delegations met and pressed Pope Francis for an apology for church-run residential schools in Canada.

Since last May, more than 1,300 unmarked graves have been uncovered at church-run schools attended by Indigenous children in Canada as part of a government program of forced assimilation. Systemic violence affected 150,000 indigenous children between 1883 to 1996. 

The Catholic Church in Canada apologized in September to the indigenous community for a century of abuse at Church-run residential schools set up by the government.

In January, Canada announced its biggest settlement of $31.5 billion to reform its discriminatory child welfare system and compensate Indigenous families who had their families broken up. 

$20 billion will be allocated for First Nations children removed from family care and enrolled in state residential schools to assimilate them.

In 2015, the Truth and Reconciliation Commission labeled the almost-century-long legacy a "cultural genocide". Children were beaten for speaking their native language, which violently compelled the Natives into cultural isolation, then genocide. 

500+ indigenous children died in US-run schools

Similarly, a report from the US Department of the Interior revealed in May that more than 500 Native American children died in US government-run boarding schools at which students were physically abused and denied food.

The report found that "approximately 19 Federal Indian boarding schools accounted for over 500 American Indian, Alaska Native, and Native Hawaiian child deaths."

"The Department expects that continued investigation will reveal the approximate number of Indian children who died at Federal Indian boarding schools to be in the thousands or tens of thousands," it mentioned.

According to the report, there are marked or unmarked burial sites at more than 50 locations, out of a total of more than 400 that made up the Federal Indian boarding school system between 1819 and 1969.

Read more: 'No Reason to Celebrate’: Tribes Mourn on Thanksgiving