Bradley Manning, the soldier sentenced to 35 years in jail for the biggest breach of official secrets in US history, says he is a woman and wants to be known as Chelsea.

"I am Chelsea Manning, I am a female," Manning, 25, said in a statement given to NBC's Today show.

"As I transition into this next phase of my life, I want everyone to know the real me.

"Given the way I feel and have felt since childhood, I want to begin hormone therapy as soon as possible.

"I also request that starting today you refer to me by my new name and use the feminine pronoun."

Manning was sentenced on Wednesday for handing more than 700,000 secret files, videos and diplomatic cables to the anti-secrecy website WikiLeaks.

Manning's lawyers had argued the former Army intelligence analyst suffered a sexual identity crisis when he leaked the files while serving in Iraq in 2009 and 2010.

Speaking on the TV show, Manning's lawyer David Coombs said he expected his client to receive a pardon from US president Barack Obama.

Manning was convicted last month on 20 charges, including espionage and theft, and will serve the sentence at the US Disciplinary Barracks at Fort Leavenworth, Kansas.

The Defence Department referred a call seeking comment to the US Army, which did not respond immediately.

Who is Bradley Manning? Born in Crescent, Oklahoma, reportedly created first website at age 10

Born in Crescent, Oklahoma, reportedly created first website at age 10 Was into computer hacking before joining the US army

Was into computer hacking before joining the US army Bullied over his homosexuality and gender identity issues

Bullied over his homosexuality and gender identity issues US army private, now aged 26, was posted to Iraq in 2009 as an intelligence analyst

US army private, now aged 26, was posted to Iraq in 2009 as an intelligence analyst Arrested in 2010 and accused of the biggest leak of government secrets in US history

Mr Coombs said Manning was seeking hormone therapy and not a sex-change operation.

"I'm hoping that Fort Leavenworth will do the right thing and provide that," he said.

"If Fort Leavenworth does not, then I'm going to do everything in my power to make sure that they are forced to do so.

"I think the ultimate goal is to be comfortable in her skin and to be the person that she's never had an opportunity to be."

Manning had not wanted his sexual identity issues to become public, but they did after his arrest in 2010, Mr Coombs said.

"Now that it is [public], unfortunately you have to deal with it in a public manner," he said.

A psychiatrist, Navy Reserve Captain David Moulton, testified during Manning's trial that he suffered from gender dysphoria, or wanting to be the opposite sex, as well as narcissism and obsessive-compulsive disorder.

Defence lawyers had argued that Manning had been increasingly isolated and under intense stress when the files were leaked, and that Manning's superiors had ignored warning signs.

They cited erratic behaviour, including sending a picture of himself dressed as a woman to a superior and punching another soldier.

Reuters