The US Army private accused of passing secret documents to WikiLeaks said Thursday he "started to fall apart" after being detained, as he took the stand for the first time in the case.

Bradley Manning, 24, looked nervous and his voice trembled slightly as he began to answer questions at a pre-trial hearing in a courtroom at Fort Meade, Maryland, north of the US capital.

Manning faces an array of serious charges that could send him to prison for life over his alleged document dump to the secret-spilling WikiLeaks website.

Defense lawyer David Coombs began with questions focused on Manning's initial detention in Iraq and Kuwait, before he was transferred to a brig at Quantico, Virginia in July 2010.

Manning said that, soon after his detention, he lost phone privileges and started to feel increasingly anxious and distressed.

"I totally started to fall apart," said the baby-faced soldier, clad in a blue dress uniform.

Manning is asking a judge to dismiss his case because of alleged illegal punishment he suffered during his pre-trial detention for nine months at the Quantico brig, where he was kept in solitary confinement for 23 hours a day.

Before his transfer to Quantico, Manning said guards at US brig in Kuwait repeatedly searched his cell and scattered his possessions.

He said he felt increasingly "hopeless."

"I was in a pretty stressed situation...I was getting very little information" from a defense attorney, he said.

Manning said he soon had suicidal thoughts, which he conveyed to mental health counselors.

"I certainly contemplated it a few times," he said.

"I had pretty much given up. My world had just shrunk."

Two US military psychiatrists testified earlier that the harsh detention conditions imposed on Manning at the Quantico brig were unnecessary and against their medical advice.

Captain William Hocter, a Navy doctor who evaluated Manning about every week during his confinement at Quantico, told the court Wednesday the suicide watch was "senseless" and that commanders consistently ignored his advice to lift tough suicide watch measures.

At Quantico, Manning had his glasses taken away, had to request toilet paper and was forced to remove his underwear at night and then sleep on an uncomfortable mattress designed for inmates deemed a suicide risk.

A UN rapporteur on torture concluded Manning was subjected to cruel and inhumane treatment at the Quantico brig.

After his detention from July 2010 to April 2011 at Quantico, Manning was transferred to a prison at Fort Leavenworth in Kansas, where authorities concluded he was not a suicide risk and was granted regular privileges.

The US military judge presiding over the case, Denise Lind, ruled Thursday that she accepted the terms under which Manning could plead guilty to some charges.

But Lind's decision focused solely on the wording of a proposal from Manning and did not represent formal acceptance of his possible plea, which could come at future proceedings.

The plea proposal from Manning would allow him to admit responsibility for leaking a trove of military intelligence logs and State Department cables, but under lesser offenses that carry less severe penalties.

Under the proposal, Manning would not face the grave charge of "aiding the enemy" which could send him to prison for life.