National security leaker Chelsea Manning is not receiving medical treatment for her gender identity condition, it has been claimed.

The American Civil Liberties Union and Manning's civilian lawyer, David Coombs, have told the US Disciplinary Barracks in Fort Leavenworth, Kansas, and officials including defence secretary Chuck Hagel, that a lawsuit will be filed if it is not confirmed by September 4 that the treatment will be provided for the army private.

Manning, who changed her name from Bradley after her conviction, is serving a 35-year sentence at Fort Leavenworth for sending classified documents to the WikiLeaks website. She has been diagnosed with gender dysphoria, the sense of being a woman in a man's body.

Manning sought evaluation and treatment after she was sent to Fort Leavenworth last September. She is asking for hormone therapy and to be able to live as a woman.

Military doctors confirmed the gender dysphoria diagnosis and recommended a treatment plan, but she has yet to receive any, according to the ACLU.

"The continued failure to provide Ms Manning with this treatment is inconsistent with well-established medical protocols and basic constitutional principles," Chase Strangio, lawyer for the ACLU's Lesbian Gay Bisexual and Transgender Project, said.

Mr Strangio said refusing to treat Manning was "cruel and unusual punishment" and accused the US Army of withholding treatment for political reasons.

The lack of treatment puts Manning at risk for serious long-term physical and psychological harm, her advocates say.

Former intelligence analyst Manning was sentenced last year for six Espionage Act violations and 14 other offences for giving WikiLeaks more than 700,000 secret military and US State Department documents.

Manning's request for treatment was the first made by a transgender military inmate. It conflicts with a policy that bans transgender people from serving in the US military, but Manning cannot be discharged from the service while serving her prison sentence.