A US Army private accused of passing a cache of confidential government documents to the secret-spilling WikiLeaks website is expected to testify during a new round of pre-trial hearings that began Tuesday.

Bradley Manning, 24, could spend the rest of his life in prison if convicted of aiding the enemy with the massive leak -- including military logs from Iraq and Afghanistan and sensitive diplomatic cables -- that embarrassed Washington and angered US allies.

The latest round of proceedings, set to last until Sunday at the Fort Meade military base near the US capital, are expected to tackle Manning's treatment in detention at Quantico military prison, shortly after his arrest in May 2010.

As protesters demonstrated Tuesday outside the base in support of Manning, the defense filed an appeal calling for the dropping of all charges, citing a section of US military code that bans "unlawful pre-trial punishment."

Manning was initially held at a US base in Kuwait after his arrest in Iraq before he was moved to Quantico in Virginia. He is expected to speak about his detention conditions on Wednesday or Thursday.

The former army intelligence analyst has complained that he was held in isolation at Quantico, was forced to strip at night and was not allowed to exercise in his cell, where he spent 23 hours a day, amid fears he could commit suicide.

"He was held in solitary confinement for nine months, conditions that the UN chief investigator on torture held inhumane and degrading," Emma Cape, one of about 30 protesters who had gathered outside Fort Meade in support of Manning, told AFP.

Manning was later transferred to a prison at Fort Leavenworth in Kansas, where he was placed under less restrictive conditions.

"If we were not here, the military might not be accountable for all the violations toward Bradley Manning," said Nathan Fuller, spokesman for a Manning support network.

The group, braving the rain, carried signs that read "Blowing the whistle on war crimes is not a crime" and "Free Bradley Manning."

Manning is scheduled to go on trial on February 4 next year.