The lawyer for Bradley Manning, the soldier accused of having leaked a massive trove of US state secrets to WikiLeaks, has accused his military jailers at the marine base in Quantico, Virginia, of ritually humiliating his client by stripping him naked in his cell every night.

David Coombs, who is representing Manning in his court martial procedure, criticised the commanders of the Quantico brig for punishing the prisoner for a sarcastic comment he made in protest at his treatment. Coombs said Manning quipped that if he wanted to harm himself he could do so with the elastic waistband in his underpants or with his flip-flops.

Though the comment was sarcastic, Coombs claims it was used by the military guards to tighten Manning's already harsh treatment under a prevention of injury order or POI. Each night since Wednesday, and for the indefinite future, Manning is forced to remove all his clothing and sleep naked in his cell, then required to endure what Coombs calls the "humiliation of standing naked at attention for the morning roll call".

Quantico is refusing to explain why it is forcing Manning to strip naked at night, citing privacy rules. But a spokesman has denied any desire to humiliate or embarrass the prisoner.

Manning has been held in solitary confinement for the past 10 months, having been arrested outside Baghdad where he was working as a military intelligence officer. He is charged with multiple counts of having downloaded classified documents and handing them to "the enemy".

For most of his time in Quantico, where he was transferred in July, he has been held under a POI order, which is a degree less severe than suicide watch. The POI requires Manning to wear just underpants and flip-flops, and to remain in his cell 23 hours a day, where he is visually checked every five minutes.

According to Coombs, Manning made his off-the-cuff comment about the elastic in his waistband in order to protest against what he regards as the "absurd" restrictions he is already under. Coombs alleges that the military jailers tightened the terms of the POI rather than imposing a suicide watch order because they knew that prison psychiatrists would never approve it.

The brig's psychiatric team has on several occasions indicated that they do not regard Manning as a mental health risk.

"The Brig's treatment of PFC Manning is shameful," Coombs said. "There is no justification for treating a detainee in this degrading and humiliating manner."