Lawyers for the US soldier on trial for passing a trove of classified documents to WikiLeaks on Tuesday accused the government of withholding emails about his pre-trial detention.

The defense team for Private Bradley Manning, who could be jailed for life for "aiding the enemy" over the WikiLeaks incident, said top officers had put their concerns about negative publicity ahead of their client's fair treatment.

The emails relate to the conditions that the 24-year-old trooper was held in at a Quantico brig in Virginia, where he was sent after a spell in a US military jail in Kuwait following his arrest when on duty in Iraq in 2010.

Manning's civilian lawyer David Coombs told a pre-trial hearing that 84 emails were released to the defense team in July last year, before it emerged that 1,290 other messages had not been passed on to him.

The government "chose to let these emails collect dust somewhere," Coombs said on the first day of the three-day hearing at a military base in Fort Meade, Maryland, 30 miles (48 kilometers) from the US capital.

The emails are "material to the defense" of Manning, Coombs told the hearing, before it emerged in open court that military prosecutors handed around 600 such messages to Manning's lawyers on Monday, ahead of the hearing.

"It is the defense position that the government has been playing word games," Coombs said, implying that the messages were held back because the government had contrived a deliberately narrow definition of their relevance to the trial.

After his detention at Quantico from July 2010 to April 2011, which sparked an uproar from rights activists, Manning was transferred to a prison at Fort Leavenworth in Kansas, where he was placed under less restrictive conditions.

The soldier's lawyers argue that Manning was mistreated after his arrest, breaching his rights. If the court finds he was abused, the case could potentially be thrown out, or any eventual sentence reduced.

Defense and prosecution lawyers have repeatedly clashed over what documents are pertinent in the case, with Manning's counsel accusing the government of hiding information that could help their client.

The court heard Tuesday that the emails went as high up the chain as General George Flynn, the then commanding general of the US Marine Corps, who had insisted that Manning be placed on suicide watch, according to Coombs.

Top officers at Quantico regularly sent emails to Flynn informing him of Manning's detention conditions, which the defense says were unnecessarily harsh.

The military "kept Manning in maximum POI (prevention of injury)" custody "because they didn't want any negative publicity," Coombs said.