Manning, 25, speaks at sentencing phase of his trial and says 'I believed I was going to help people, not hurt people'

Bradley Manning, the soldier convicted last month of leaking an enormous collection of classified documents to WikiLeaks, has said he now regrets his actions and that he was "sorry that they hurt the United States".

"I am sorry for unintended consequence of my actions. When I made these decisions, I believed I was going to help people, not hurt people," Manning told his sentencing hearing, in an attempt to receive a reduced sentence.

The 25-year-old was found guilty of several counts under the Espionage Act, but acquitted of the most serious charge of "aiding the enemy". He is facing a possible jail sentence of up to 90 years when he is sentenced next week.

Previously, the former intelligence analyst tried to justify his actions, explaining to the court in detail how he downloaded 700,000 classified documents while stationed in Iraq and passed them to the anti-secrecy website, in order to prompt a global debate about the wars in Iraq and Afghanistan.

However on Wednesday, after three days in which his legal team called witnesses they hoped would lead to a lower sentence, Manning took to the stand for an unsworn statement – meaning he could speak to the judge but not be cross-examined.

Looking nervous, he turned to Colonel Denise Lind, who is presiding over his court martial, and said: "First, your honour, I want to start off with an apology. I am sorry that my actions hurt people. I am sorry that I hurt the United States."

He told the military judge that he "was dealing with a lot of issues" around the time he leaked the classified material, problems that he continues to effect him.

"Although a considerable difficulty in my life, these issues are not an excuse for my actions," he said. "I understood what I was doing, and decisions I made. However I did not fully appreciate the broader effects of my actions.

"Those factors are clear to me now, through both self-refection during my confinement in various forms, and through the merits and sentencing testimony that I have seen here.

"I am sorry for the unintended consequences of my actions," he continued. "When I made these decisions I believed I was going to help people, not hurt people."

The soldier read out his statement in a rushed fashion, looking anxious. He told the judge that he had learned from his experience and asked for a chance to rebuild his life.

The apology will disappoint Manning's thousands of supporters around the world, who believe he undertook a courageous act of whistleblowing because his conscience demanded it.

Manning has achieved folk-hero status in some quarters, as the first data mass leaker of his kind, comparable to Edward Snowden, the former National Security Agency who recently disclosed documents about US surveillance activities.

Some of his supporters at the courthouse looked forlorn and were in tears – but pointed out he was facing almost 100 years in prison and had to do everything to seek a reduction in his punishment.

In one line certain to upset those who believe Manning made a positive difference by leaking the documents, he said he now looks back at his decisions and wonders "how on earth could I, a junior analyst, possibly believe I could change the world for the better".

Manning said that he "had options" other than leaking the documents, and he "should have worked more aggressively in the system", adding: "Unfortunately, I can't go back and change things."

"I understand I must pay a price for my decisions and actions," he said, adding he wanted to become a better person, go to college and get a degree, and establish a "meaningful" relationship with his sister.

"I have flaws and issues that I have to deal with, but I know that I can and will be a better person," he said. "I hope that you can give me the opportunity to prove, not through words, but through conduct, that I am a good person and that I can return to productive place in society."

Moments earlier, Manning's sister, Casey Major, provided the court with an insight of their difficult upbringing with two alcoholic parents. Major, 36, said that while her father, Brian, was a "functional alcoholic", who could get up to work after drinking, her mother, Susan, had a more serious problem.

She said her mother drank hard liquor from around lunchtime, and would often continue through the night until she had passed out. Asked how often she was drunk, Major replied: "At least every day."

Their mother would often wake-up in a terrible mood, Major said. "She was mean, very mean, yelled, screamed at you, to get her cigarettes, or make her a cup of tea."

She said her mother drunk through her pregnancy with Manning and, when he was born, it often fell to Major, then aged eleven, to look after her infant brother.

When Manning was 12, their father left the family home. One night her mother attempted suicide, and Major recalled how when they got into the family car in their rural home in Oklahoma to drive to the hospital, their father refused to sit on the back seat to monitor their mother.

"Unfortunately my 12 year old brother had to go back there and check his mom was breathing for the whole car ride," she said. After that incident, she said her mother threatened to kill herself "every day".

The court heard from another witness on Wednesday that, from childhood, Manning began to have feelings that would eventually lead to a diagnosis of gender dysphoria, which occurs when an individual feels they belong to the opposite gender.

Navy Captain David Moulton, a forensic psychiatrist who spent over 100 hours interviewing Manning and reviewing his medical records, said the soldier's decision-making ability was "impaired" by the stress he underwent in Iraq trying to cope with his gender identity crisis.

He said that Manning, who could not seek assistance for his problems in the military, was suffering from serious stress when he chose to download and then leak hundreds of thousands of documents to WikiLeaks.

"His decision-making capacity at that point I think was influenced by the stress of his situation, for sure," he said.

The psychiatrist added that Manning's ability to "rationally" consider the consequences of his actions was also impeded. The soldier assumed he would merely be thrown out of the military, an assessment the psychiatrist described as a "gross underestimation".

Manning told the psychiatrist that, if he had had a friend to talk through his moral dilemmas, "that might have prevented these acts".

Another defence witness, Captain Michael Worsley, a clinical psychologist who evaluated and treated Manning between December 2009 and May 2010, when he was stationed in Iraq, said the pressure Manning faced "would have been incredible".

"I think being in the military and having a gender identity issues does not exactly go hand in hand," he said.