Canadian Prime Minister Justin Trudeau on Monday expressed grief while pledging "concrete action" in support of indigenous communities after the remains of 215 indigenous children were discovered at an old boarding school.

During a news conference, Trudeau said he his appalled at the shameful policy that ripped indigenous children from their families. "As a dad, I can't imagine what it would feel like to have my kids taken away from me."

Canadian PM pledges action over mass indigenous student grave

"Think of their communities that never saw them again. Think of their hopes, their dreams, their potential, of all they would have accomplished, all they would have become," he said. "All of that was taken away."

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Since 2015, when he came to power, Trudeau had made reconciliation with Canada's nearly 1.7 million indigenous people a priority of his government. The Truth and Reconciliation Commission of Canada concluded the country committed "cultural genocide" with its decades-long residential school system.

He said he plans to speak with his three cabinet ministers to shore up "next and further things we need to do to support (residential school) survivors and the community."Excavating school burial sites across Canada, as many have urged, he also said, "is an important part of discovering the truth."

"Canada will be there to support indigenous communities as we discover the extent of this trauma and trying to give opportunities for families and communities to heal."

The Kamloops Indian Residential School was operated by the Catholic church on behalf of the Canadian government from 1890 to 1969 before Ottawa took over its administration and closed it a decade later. It was the largest of 139 boarding schools set up in the late 19th century to assimilate Canada's indigenous people, with up to 500 students registered and attending at any one time.

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The official records show only 50 deaths at the school, where a principal once pleaded for more funds to properly feed students.

Flags atop government buildings were lowered to half-mast over the weekend, including the Peace Tower on Parliament in Ottawa, as the nation mourned.

In Ottawa, row upon row of children's shoes was left in front of parliament and on steps outside government offices and churches in several cities, forming makeshift memorials.

About 100 people marched on Sunday, several in ceremonial attire in the Mohawk community of Kahnawake, near Montreal.

Perry Bellegarde, National Chief of the Assembly of First Nations said the former students and families "deserve to know the truth", quoted by the Globe and Mail.  "A thorough investigation into all former residential school sites could lead to more truths of the genocide against our people," he added.

The British Columbia coroner is helping the Tk'emlups te Secwepemc tribe establish the causes and timings of the student deaths in Kamloops.

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Federal New Democrats are calling for an emergency debate in parliament on the "heart-breaking" discovery. 

Around 150,000 Indian, Inuit, and Metis youngsters in total were forcibly enrolled in these schools, where students were physically and sexually abused by headmasters and teachers who stripped them of their culture and language.

To this very day, the experiences are blamed for a high incidence of alcoholism, poverty, and domestic violence, as well as high suicide rates, in indigenous communities.

As of now, the truth and reconciliation commission has identified the names and dig out information about, at least 4,100 children who died from abuse or neglect while attending a residential school. It estimates the actual toll is much higher.

In 2015, the commission report had concluded that more than a century of abuses at the schools amounted to "cultural genocide." 

Meanwhile, the National Centre for Truth and Reconciliation at the University of Manitoba has set up an online registry with the names of the thousands of children who never came home from the boarding schools, along with old class photos.