'How can you apologise for a genocide while committing a genocide?'

US President Joe Biden was heckled at the event over his support for Israel's genocidal war in Gaza as he formally apologised for the US government's role in running abusive Native American boarding schools for more than 150 years.

"This to me is one of the most consequential things I've ever had an opportunity to do in my whole career," Biden said in his apology at an outdoor football and track field in Laveen Village, Arizona, near Phoenix on Friday.

"It's a sin on our soul. ... I formally apologise."

Several hundred people attended, many of them in traditional tribal dress. They cheered as Biden apologised for the generational trauma faced by the Native American community due to the boarding schools across the country.

Biden faced an interruption when a pro-Palestinian protester shouted: "How can you apologise for a genocide while committing a genocide in Palestine?"

The president replied, "There is a lot of innocent people being killed and it has to stop."

US support for Israel's wars in Gaza and Lebanon has led to months of demonstrations across the United States. There have been widespread calls for an arms embargo against Israel as tens of thousands of civilians have been killed by Israel in the region, and Palestinians in Gaza have grappled with hunger and disease due to Israeli siege.

Genocide allegations have been brought against Israel at the World Court in relation to Gaza, but the Biden administration has maintained its support for the Netanyahu regime.

Friday's trip marked Biden's first time visiting Indian Country while in office and is part of his effort to cement his legacy in his final months in the White House.

Arizona is also one of the seven battleground states in a tight race for the November 5 US election in which Democratic Vice President Kamala Harris faces Republican former President Donald Trump.

Reviewing past abuse

US Interior Secretary Deb Haaland, the first Native American to be a cabinet secretary, had launched an investigation to recognise the troubled legacy of federal Native American boarding school policies.

An Interior Department investigative report released in July found that at least 973 children died in these schools. Haaland's family members were among the children forced into the boarding schools.

From 1819 through the 1970s, the United States implemented policies establishing and supporting hundreds of American Indian boarding schools across the US. Their purpose was to culturally assimilate Native Americans by forcibly removing them from their families, communities, religions, and cultural beliefs.

Like the United States, Australia, New Zealand and Canada have in recent years reviewed past abuse toward Indigenous communities, including children in schools.