Bradley Manning, the 22-year-old US Army private accused of handing classified information to WikiLeaks, has been subjected to conditions since his arrest that would constitute torture in many nations - despite never having been convicted of any crime.

According to an article by commentator Glenn Greenwald at Salon.com, Manning is reported to have been a "model prisoner" since his arrest in May - and yet has been been subjected to conditions Greenwald says are "likely to create long-term psychological injuries".

Manning, who served in Iraq, is accused of passing classified documents to whistle-blowing web site WikiLeaks, including video footage of a US helicopter airstrike that the site termed the "murder of Iraqi civilians and two Reuters journalists".

WikiLeaks founder Julian Assange - himself currently in custody in the UK - has refused to identify the source of the leaks, but has said that if Manning were responsible he would be an "unparalleled hero".

In an outspoken attack on what he calls "the dark side of American exceptionalism", Greenwald claims that Manning has been "subjected for many months without pause to inhumane, personality-erasing, soul-destroying, insanity-inducing conditions of isolation."

Manning has been held at the US Marine brig in Quantico, Virginia, for five months. Before that, he spent two months in a military jail in Kuwait. From the outset, he has been declared a "Maximum Custody Detainee" - the most restrictive level of US military detention.

Reports from a number of sources directly familiar with Manning's conditions indicate that from the beginning of his detention, he has been kept locked up in solitary confinement for 23 hours a day.

Conditions inside his cell are also heavily restricted. Manning is not allowed to exercise. And despite never having been on suicide watch, he is allowed neither a pillow nor sheets on his bed.

Quantico brig official Lt Brian Villiard has denied reports that Manning is prevented from accessing any news or current affairs programmes during the one hour each day he is released from his confinement. But sources close to the case confirmed that Manning is now being regularly prescribed anti-depressant medication to mitigate the effects of his inhuman treatment.

Greenwald cites the opinion of surgeon and journalist Atul Gawande, expressed in a 2009 New Yorker article, that "all human beings experience isolation as torture".

He also points to medical research conducted in 1992 on Yugoslavian prisoners of war kept in solitary confinement for an average of six months - around the length of time Manning has so far served - which uncovered evidence of severe brain abnormalities months after their release.

"Without sustained social interaction," the report concluded, "the human brain may become as impaired as one that has incurred a traumatic injury."

Historically, US civilian courts have taken a dim view of solitary confinement, with a landmark 1940 decision in the case of Chambers v Florida labelling the practice "torture".

Manning is expected to face a military court-martial early in 2011.

If found guilty, he may face the death penalty.