Former US Army soldier and whistleblower Chelsea Manning has tried to commit suicide for a second time last month, her lawyers said.

Manning, 28, the former Army intelligence analyst who is serving a 35-year sentence for leaking archives of secret documents to WikiLeaks, attempted to kill herself after she was sentenced to 14 days in solitary confinement in September, her punishment for a previous attempt to end her life in July.

Manning is a transgender former Army intelligence analyst who was born Bradley Manning.

Her lawyer, Chase Strangio confirmed the attempt, which raised new questions about the military's handling of the troubled soldier, dating to her time she was permitted to serve in Iraq.

Strangio, an American Civil Liberties Union lawyer said his client has tolerated a long series of "demoralizing" and "destabilizing" assaults on her health and her humanity.

"I worry about the sustainability of her current conditions and her ability to keep fighting under these relentless abuses," he added.

According to Dr. Stuart Grassian, a psychiatrist who is a specialist in the psychiatric effects of solitary confinement, it was a "mistake" by the US military to place such "fragile people with mental illness" in solitary confinement.

Manning disclosed diplomatic cables from American embassies around the world, incident logs from the Afghanistan and Iraq wars, intelligence on Guantánamo Bay detainees and a video of a helicopter airstrike in Baghdad in which two Reuters journalists were killed.

She leaked classified info to WikiLeaks in early 2010, which made her a hero to open-government activists.