Supporters claim the war logs leak exposed civilian deaths in Afghanistan which had been covered up by the military, and Mr Manning's family, who live in Pembrokeshire, said he had "done the right thing".

The Pentagon, which is investigating the source of the leak, is expected to study Mr Manning’s background to ascertain if they missed any warnings when he applied to join the US Army. The postings on his Facebook page are also likely to form part of the inquiry.

Mr Manning, who is openly homosexual, began his gloomy postings on January 12, saying: "Bradley Manning didn't want this fight. Too much to lose, too fast."

At the beginning of May, when he was serving at a US military base near Baghdad, he changed his status to: "Bradley Manning is now left with the sinking feeling that he doesn't have anything left."

Five days later he said he was "livid" after being "lectured by ex-boyfriend", then later the same day said he was "not a piece of equipment" and was "beyond frustrated with people and society at large".

His tagline on his personal page reads: "Take me for who I am, or face the consequences!"

Mr Manning was arrested at the end of May on suspicion of leaking a video of a US helicopter attack, and quickly became the main suspect when the Afghan war documents were leaked earlier this week.

His uncle, Kevin Fox, said the soldier’s arrest and imprisonment in a military jail had taken its toll on his mother Susan, who lives in Haverfordwest.

“She hasn’t been well,” he said, adding that if Mr Manning had leaked the documents: “I think the boy did the right thing.”

Another close relative, who asked not to be named, said: “His mum didn't know anything about what he was doing and it's come as a big shock. She's very upset.”

Susan Manning, 56, moved to the US in 1979 after marrying Bradley’s American father Brian Manning, a former serviceman who was based at the Cawdor Barracks in Brawdy, near Haverfordwest.

Bradley Manning was born in Oklahoma but the couple divorced in 2001 and Mrs Manning moved back to Wales with her son, who sat his GCSEs at the Tasker Milward secondary school in Haverfordwest.

Joseph Staples, Mr Manning's uncle by marriage, said: “It's one of those Catch 22 situations, because freedom of speech is great but if you do something that endangers other people's lives then I can understand why you're going to get flattened by the American military.

“Some people are saying that Bradley was a trouble-maker but he was anything but. He was just an introverted kid who loved computers and was fired up politically.”

Scott Lewis, a former classmate, said: "He was a bit hot-headed. If there was something he didn't agree with, he spoke up about it."

Other school contemporaries recalled him as a computer “nerd” who had a difficult relationship with his father.

Jenna Morris, a 23-year-old sales manager who went on holiday to Disney World in Florida with Bradley and his cousins, said: “He was a quiet lad and he’d had a tough upbringing.

“His parents had an acrimonious divorce. He didn’t get on well with his dad; they had quite a volatile relationship. His dad was very strict and shouted at him a lot.

“He had a tough time when he came back here with his mum because moving to another country after a break-up was hard. He was quite a loner and he didn’t really have a lot of friends. He had quite a bit of trouble at school and was picked on, but he didn’t care.”

James Kirkpatrick, who became friendly with him through their shared interest in computers, said: “I last contacted him about six months ago. He didn’t mention anything about what was happening, but at the same time he did seem a bit secretive, he was being a bit paranoid about what we spoke about on the net.

“He wouldn’t mention anything about what he was doing in the army and what he thought of it.”

Pictures on Mr Manning's Facebook page include photos of him on school trips during his time in Wales and at a gay rights rally, where he is holding up a placard demanding equality on "the battlefield".

Yesterday Mr Manning, who is reportedly on suicide watch, was transferred from a military jail in Kuwait to a prison in Washington DC, as the Pentagon called in the FBI to assist in the hunt for the source of the leak.

Admiral Mike Mullen, the chairman of the US military's Joint Chiefs of Staff, said the leakers “might already have on their hands the blood of some young soldier or that of an Afghan family” because, he said, the leaked documents included the names of Afghan informants.