Bradley Manning, a young American soldier suspected of leaking a massive trove of secret US documents, has become a hero to anti-war activists and a villain to government officials outraged over the exposure of classified files.

The WikiLeaks website has yet to reveal how it obtained hundreds of thousands of secret documents in recent months, including more than 250,000 diplomatic cables published this week.

But suspicions have centered on the 23-year-old Manning, the baby-faced private who was arrested in May after WikiLeaks released a video showing a 2007 US Apache helicopter strike in Baghdad.

A native of Oklahoma who later moved to Wales, Manning reportedly was taunted by other children for being a "geek" and as a youth in Britain endured ridicule from classmates for being gay. As a young man, his father kicked him out of the house when he learned his son's sexual orientation.

In 2007, he joined the US Army and trained as an intelligence analyst, before deploying with the 10th Mountain Division to a base near Baghdad.

In Iraq, he had to conceal his homosexuality under the military's ban on openly gay troops, known as "Don't Ask, Don't Tell."

Manning opposed the law and spoke to his friends about his sentiments, said Jeff Paterson, a member of a support network backing the soldier, who remains under detention at the Quantico Marine base in Virginia.

Manning could "identify" with Iraqis and Afghans who he believed had suffered as a result of US policies, especially because he himself was a "a member of a minority" treated unfairly by the military, he told AFP.

His friends and those who grew up with him describe a young man who struggled to find acceptance, according to The New York Times, with Manning's ambitions in the Army frustrated as officers asked him to perform menial tasks.

In the Army, he was reportedly reprimanded for assaulting an officer, resulting in a demotion from specialist to private first class.

As a low-ranking intelligence analyst, he had access to a vast archive of sensitive documents on the military's classified computer network, SIPRnet or the Secret Internet Protocol Router Network.

In online conversations published in the magazine Wired, with a former hacker, Adrian Lamo, Manning said "let's just say 'someone' I know intimately well, has been penetrating US classified networks," and transferring the data "to a crazy white-haired Aussie who can't seem to stay in one country very long," an apparent reference to Julian Assange, founder of WikiLeaks.

Manning told Lamo his motive was to expose the "truth."

"I want people to see the truth... because without information, you cannot make informed decisions as a public," he said, according to Lamo, who turned over the online chatlogs to the authorities.

Manning said that he would take a CD "labelled with something like 'Lady Gaga,'" erase the music and download a stream of classified information.

"Hillary Clinton and several thousand diplomats around the world are going to have a heart attack when they wake up one morning and find an entire repository of classified foreign policy is available, in searchable format, to the public," he wrote to Lamo.

Manning, who is being held in solitary confinement, is charged with eight violations of federal criminal law, including transmitting classified information to a third party, and two counts under military law.

Manning is accused of "transferring classified data onto his personal computer and adding unauthorized software to a classified computer system," and illegally acquiring more than 150,000 State Department cables, according to the charge sheets.

If found guilty, Manning faces up to 52 years in prison.