US President Joe Biden issued a historic apology on Friday for one of the nation’s "most horrific chapters": the abduction of Native American children from their families and their placement in government-run boarding schools aimed at erasing their cultural identities.

From the early 1800s to the 1970s, the United States ran hundreds of Indian boarding schools across the country, aiming to forcibly assimilate Native children into European settler culture, including attempts to convert them to Christianity.

A recent government report revealed alarming instances of physical, mental, and sexual abuse, alongside the deaths of nearly a thousand children.

In a speech at the Gila River Indian Community in Laveen Village, Biden said "I formally apologize, as president of the United States of America, for what we did."

He described the approximately 150 years during which the school system operated as one of the "most horrific chapters in American history" and labeled it a "sin on our soul."

"I know no apology can or will make up for what was lost during the darkness of the federal boarding school policy," he continued.

"Today, we're finally moving forward into the light."

More than 973 children killed in US boarding schools

At least 973 Native American children died under the US government's abusive boarding school system, an investigation commissioned by US Interior Secretary Deb Haaland by officials revealed on July 31, as they urged the government to issue a formal apology for the schools.

The probe found marked and unmarked graves at 65 of the over 400  US Native American boarding schools where children of the minority group were forcibly assimilated into white society. Although the investigation did not disclose descriptions of each child's death, officials said the causes of death included sickness and abuse that lasted for 150 years, ending in 1969. In addition, children may have also passed away at home after contracting illnesses at the boarding school.

"The federal government took deliberate and strategic action through boarding school policies to isolate children from their families, deny them their identities, and steal from them the languages, cultures and connections that are foundational to Native people," Haaland, the first Native American cabinet secretary and Laguna Pueblo tribe member, told reporters on Tuesday, adding the system was established "to eradicate the, quote, ‘Indian problem,’ to either assimilate or destroy native peoples altogether."

Last year in August, the National Native American Boarding School Healing Coalition uncovered 115 more institutions than the previous 408 federally recognized ones, increasing the total number of schools that forced Native American children to assimilate into White culture in the United States to 523.