AN UNPRECEDENTED study of Native American boarding schools that, for over a century, sought to assimilate indigenous children into white US society has identified more than 500 pupil deaths at the institutions.

Published on Wednesday, the report by the federal Interior Department expands to more than 400 the number of schools that were established or supported by the government, starting in the early 19th century and continuing in some cases until the late 1960s. The agency identified the deaths in records for about 20 of the schools.

The dark history of Native American boarding schools, where children were forced from their families, prohibited from speaking their languages and often abused, has long been felt deeply in indigenous communities.

Many children never returned home and the Interior Department said that, with further investigation the number of known pupil deaths could climb to the thousands or even tens of thousands. Causes included abuse, disease and accidental injuries.

“Each of those children is a missing family member, a person who was not able to live out their purpose on this Earth because they lost their lives as part of this terrible system,” said Interior Secretary Deb Haaland, whose paternal grandparents were sent to boarding school for several years.

The agency is poring through thousands of boxes containing more than 98 million pages of records, with help from many indigenous people. Determining the total number of deaths will be difficult because records weren’t always kept.

A second volume of the report will cover burial sites, the federal government’s financial investment in the schools and the impacts on indigenous communities, the Interior Department said.

A US House of Representatives subcommittee was due to hear testimony lasts night on legislation to create a truth and healing commission modelled on one already set up in Canada.