The Canadian government demanded all flags at federal buildings be lowered to half-mast on Sunday to commemorate the death of over 200 indigenous children.
A mass grave containing the remains of 215 indigenous children was discovered on the grounds of a former residential school in British Columbia.
Canadian Prime Minister Justin Trudeau said it was a "painful reminder" of a "shameful chapter of our country's history".
"To honour the 215 children whose lives were taken at the former Kamloops residential school and all Indigenous children who never made it home, the survivors, and their families, I have asked that the Peace Tower flags and flags on all federal buildings be flown at half-mast," he wrote on Twitter on Sunday.
The discovery was announced on Thursday by the chief of the Tk'emlups te Secwepemc First Nation.
"To our knowledge, these missing children are undocumented deaths," Kukpi7 chief Rosanne Casimir said in a press statement.
"Some of these were as young as three years old.
"We sought out a way to confirm that knowing out of deepest respect and love for those lost children and their families, understanding that Tk'emlúps te Secwépemc is the final resting place of these children."
The Kamloops Indian Residential School was established in 1890 under the leadership of the Roman Catholic Church and closed in 1978.
Children were forcibly removed from their homes and were not allowed to speak their native language as part of the government policy of forced assimilation.
Physical, emotional and sexual abuse were prevalent within these institutions.
"There is so much grief and trauma from the horrific news of the 215 children's bodies being found," New Democratic Party parliament member Charlie Angus tweeted on Sunday.
"I am pleased that the Prime Minister has agreed to lower the flags. But this is just the beginning. We need answers. We need accountability."