In one of his final acts before leaving office, President Barack Obama has commuted the prison sentence of Chelsea Manning, the former US military intelligence analyst behind the biggest breach of classified materials in US history.

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Manning has been a focus of a worldwide debate on government secrecy since she provided more than 700,000 documents, videos, diplomatic cables and battlefield accounts to the anti-secrecy group WikiLeaks - a leak for which she was sentenced to serve 35 years in prison.

Manning, formerly known as US Army Private First Class Bradley Manning, was born male but revealed after being convicted of espionage that she identifies as a woman.

Manning, who is held at the Fort Leavenworth, Kansas, military prison, accepted responsibility for leaking the material, and has said she was confronting gender dysphoria at the time of the leaks while deployed in Iraq. Her sentence will now expire on May 17, the White House said.

Manning was working as an intelligence analyst in Baghdad in 2010 when she gave WikiLeaks a trove of diplomatic cables and battlefield accounts that included a 2007 gunsight video of a US Apache helicopter firing at suspected insurgents in Iraq, killing a dozen people including two Reuters news staff.

Her attorney had argued her sentence exceeded international legal norms, and she has twice attempted suicide.