Lawyers for the US soldier charged with passing a trove of classified documents to WikiLeaks accused the military Tuesday of withholding hundreds of emails over fears of a publicity nightmare.

The defense team for Private Bradley Manning, who could be jailed for life for "aiding the enemy" over the massive security breach, alleged that more than 1,300 messages were ignored by prosecutors for at least six months.

The emails relate to the conditions the 24-year-old trooper was held in during military detention at Quantico, Virginia, where he was sent after a spell in a US Army jail in Kuwait following his arrest while 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 on July 25, but he later discovered that 1,290 other messages remained on file.

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.

Military prosecutors then suddenly announced that 600 other messages had been handed to Manning's legal team on Monday, ahead of the hearing, but Coombs persisted with his attack.

"It is the defense position that the government has been playing word games," the lawyer said, implying that the emails were held back because the government adopted a deliberately narrow definition of their relevance.

"That is the absurd nature of that excuse. That is 'the dog ate my homework' excuse," Coombs added.

The defense maintains that Manning was mistreated at Quantico, and even alleged Tuesday that the former intelligence analyst had been ordered by guards to stand at attention while completely naked.

Coombs then took aim at top Marine officers responsible for running the jail, who he said had put their concerns about bad publicity ahead of their duty to provide fair treatment to detainees.

The emails go as high up the chain as General George Flynn, the then commanding general of the US Marine Corps, who insisted that Manning be placed on suicide watch.

Top officers at Quantico regularly sent emails to Flynn informing him of Manning's confinement, which the defense says was unnecessarily harsh, and told the Marine commander who the jailed WikiLeaks suspect's visitors were.

"They didn't want any negative publicity," Coombs said, reading out an official list that placed media risks at the top of eight concerns at Quantico.

After his detention at the Marine Corps Brig from July 2010 to April 2011, Manning was transferred to a prison at Fort Leavenworth in Kansas, where he was placed under less restrictive conditions.

If the court finds he was abused, the case could potentially be thrown out, or any eventual sentence reduced.

However, Major Ashden Fein, lead counsel for the government at Fort Meade, denied that the emails were withheld, insisting the prosecution simply had more pressing issues to deal with.

Most of the emails amount to nothing more than "argument and conjecture" among the military commanders involved, he said.

"They were concerned about public affairs (media handling) but they were also concerned about Private First Class Manning," Fein said of officers at Quantico, describing Flynn as "being informed but not necessarily directing" control.

Colonel Denise Lind, the case judge, however said the months-long delay over disclosure of the emails remained unexplained.

"I still wonder why you waited until July," Lind asked Fein, before ruling that she would examine the estimated 700 emails from the original bundle that remain in government hands, before deciding if they too should be handed over.

The publishing by WikiLeaks of official documents, including military logs concerning the wars in Iraq and Afghanistan, triggered a diplomatic firestorm that hugely embarrassed American officials and rankled the nation's allies.

Manning, who is attending this week's hearing, has not yet entered a plea in the case and his trial now looks set to start in February -- five months later than originally thought.