The trial of a US soldier accused of feeding classified documents to Wikileaks is to be delayed further due to debate over whether he was subjected to unlawful confinement, a military judge said Sunday.

Pfc Bradley Manning has been behind bars since his arrest in Baghdad in May 2010 on suspicion of being responsible for the largest leak of state secrets in US history.

But an attempt by his lawyers to get charges thrown out on grounds that the suspect has already been subjected to unfair punishment while in confinement looks set to lengthen his time on remand. Military judge Colonel Denise Lind announced Sunday that Manning's trial, which had been set to begin on 4 February, would now take place from 16 March at the earliest.

Lind is currently hearing evidence relating to restrictions placed on Manning during a nine month stint in military cells in Quantico, Virginia. Defence lawyers have claimed that the extreme custodial regime he was placed under – which included being confined to a 6ft-by-8ft cell for all but 20 minutes every day and being deprived of his clothes at night – amounted to unlawful pre-trial punishment.

Psychiatrists have testified that the brig commander in Quantico kept Manning under these harsh conditions despite their recommendations to ease them.

During the current sessions, Manning has spoken about the trauma he experienced while incarcerated and the effect that long periods of isolation had on him.

"I'm generally a pretty socially extrovert person, but being for long periods of time by myself I was in a pretty stressed situation. I began to really deteriorate. I was anxious all the time, everything became more insular," he said

Prosecutors have argued that the conditions in Quantico – which also included being under constant observation from guards – were necessary as Manning was a suicide risk. They showed the court a pink sheet that he had fashioned into a noose.

The article 13 hearing current taking place is just one of several ways in which Manning and his defence team are seeking to reduce the severity of any possible sentence. Under the most severe of the 22 counts he faces – "aiding the enemy" – he could be detained in military custody for the rest of his life.

In the hope of avoiding that fate, Manning has effectively admitted that he transferred government information to WikiLeaks while he was working as an intelligence analyst in Iraq.