Marked or unmarked burial sites were found at around 53 different Native American boarding schools across the United States as part of an investigation by the Interior Department into the "troubled legacy" of the institutions, which removed thousands of children from their homes.

An initial analysis found that 19 schools accounted for 500 deaths during a 150-year period. Many of the bodies were buried hundreds or thousands of miles away from their communities, according to an investigative report released Wednesday.

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"The consequences of federal Indian boarding school policies, including the intergenerational trauma caused by the family separation and cultural eradication inflicted upon generations of children as young as 4 years old, are heartbreaking and undeniable," said Secretary of the Interior Deb Haaland, the first Native to serve as a Cabinet head.

The first-ever inventory of federal Native boarding schools found that between 1819 to 1969, there were 408 schools across 37 states, including 21 schools in Alaska and seven in Hawaii. The estimate is higher than previous research indicated.

All of the schools received federal money and were operated by the government or churches. Families were forced to send their children to the boarding schools, which sought to assimilate American Indian, Alaska Native, and Native Hawaiian children through education, including by giving them English names, cutting their hair, and preventing cultural practices.

The investigation will continue through a new $7 million investment from Congress, a press release detailed. Haaland also announced a yearlong tour across the country to speak to survivors of the boarding schools and document oral histories.

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Haaland commissioned the investigation last June after the Canadian government discovered 215 unmarked graves of children who attended similar schools in Canada.

"Our children had names. Our children had families. Our children have their own languages," Haaland said, according to the Associated Press. "Our children had their own regalia, prayers, and religion before Indian boarding schools violently took them away."