The US soldier who was sentenced as Bradley Manning on Wednesday plans to undergo hormone therapy and has asked to be recognised as a woman.
In a statement on Thursday Manning said she would like to be known as Chelsea E Manning and be referred to by female pronouns.
"As I transition into this next phase of my life, I want everyone to know the real me," she wrote.
"I am Chelsea Manning. I am a female. Given the way that I feel, and have felt since childhood, I want to begin hormone therapy as soon as possible. I hope that you will support me in this transition."
But Fort Leavenworth military prison in Kansas, where Manning is due to serve out her sentence, said on Thursday that it would not provide trans treatment beyond psychiatric support, in a move criticised as unconstitutional by activists and LGBT groups.
Manning was sentenced to 35 years in prison on Wednesday for leaking hundreds of thousands of classified documents. She was found guilty of 20 counts, six of them under the Espionage Act, but her lawyers argued during the trial that Manning was acting out of a sense of duty to her country.
"I also request that, starting today, you refer to me by my new name and use the feminine pronoun (except in official mail to the confinement facility)," Manning's statement read. "I look forward to receiving letters from supporters and having the opportunity to write back."
She thanked her supporters for helping to "keep me strong" during her arrest and trial and for funding her defense.
During her trial it emerged that Manning had emailed a picture of herself, wearing a long blonde wig and lipstick, to her supervisor. In the subject line Manning had written: "My Problem".
Manning's lawyers argued that this was an example of how the soldier's supervisors failed her on numerous occasions and contributed to the stress she was under.
"The stress that [she] was under was mostly to give context to what was going on at the time," Manning's lawyer, David Coombs, told NBC's Today show on Thursday.
"It was never an excuse because that's not what drove [her] actions. What drove [her] actions was a strong moral compass."
Manning has already spent three and a half years in prison awaiting trial.Her sentence was reduced by 112 days in January after a judge ruled she had been subjected to excessively harsh treatment in military detention.
Coombs has confirmed that Manning will spend her sentence at Fort Leavenworth military prison, however a spokeswoman for the prison said this week that treatment for inmates at the prison does not include hormone therapy.
"All inmates are considered soldiers and are treated as such with access to mental health professionals, including a psychiatrist, psychologist, social workers and behavioral science noncommissioned officers with experience in addressing the needs of military personnel in pre- and post-trial confinement," Kimberly Lewis told Courthouse News Service.
"The army does not provide hormone therapy or sex-reassignment surgery for gender identity disorder."
Coombs said on Thursday that he is "hoping" that Fort Leavenworth "would do the right thing" and provide hormone therapy.
"If Fort Leavenworth does not, then I'm going to do everything in my power to make sure they are forced to do so."
Trans and civil liberties groups said it would be "unconstitutional" for Fort Leavenworth not to give Manning treatment.
"This is the United States. We do not deny medical treatment to prisoners," said Mara Keisling, executive director of the National National Center for Transgender Equality.
"It is illegal, it's unconstitutional. That is fairly settled law under the eighth amendment against cruel and unusual punishment. The medical community is now unified that transition-related care is legitimate medical care that can successfully treat a serious underlying condition."
The American Civil Liberties Union said Manning had been diagnosed with gender dysphoria and should receive hormone therapy. Statements by Fort Leavenworth to the contrary raise "serious constitutional concerns", said Chase Strangio, an attorney with the union's LGBT project.
"The official policy of the Federal Bureau of Prisons and most state agencies is to provide medically necessary care for the treatment of gender dysphoria, and courts have consistently found that denying such care to prisoners based on blanket exclusions violates the eighth amendment of the constitution."
Aside from the issue of treatment, Keisling said there was a "systemic problem" with how the justice system treats trans people, who she said face a "heightened amount of sexual assault" in both federal and military prisons.
"Trans people tend to be treated unfairly in terms of arrests, in terms of prosecution, in terms of conviction, sentencing and their time in jails and prison. It's a dramatically serious problem that Americans don't know about."
Trans prisoners should undergo an "individualised assessment", she said, to determine how they should be incarcerated.
"It is a much more complicated than trans women should be in women's prisons and trans men should be in men's prisons.
"They should take into account what will be more safe for the prisoner. They need to look at things like a prisoners' past history of being a victim or of victimising other people.
"They need to look at the person's self-assessment of where they would be safe. They need to look at a person's gender identity, they need to look at a person's sexual orientation."