A US military judge said she will rule later today on a motion to dismiss all charges against a soldier charged with sending thousands of classified documents to the WikiLeaks secrets-spilling website.

Bradley Manning, a 24-year-old former Army intelligence analyst, argues that the military held him in unduly harsh conditions for nine months to punish him after his 2010 arrest.

The Defence Department has said Manning was a suicide risk and that it was only trying to keep him from hurting himself and others when it confined him to a tiny, windowless cell for 23 hours a day.

Legal experts say the chances of the case being thrown out are slim, but Manning could win extra credit for the time he has already served if he is convicted at a court martial and sentenced to prison.

He faces 22 charges, including aiding the enemy, which carries a maximum of life behind bars. The current pretrial hearing focuses on whether Manning's motivation matters in the case.

Prosecutors want the judge to bar the defence from producing evidence at the March 6 trial regarding his motive for allegedly leaking hundreds of thousands of secret war logs and diplomatic cables.

Manning allegedly told an online confidant he leaked the material because he wanted people to see the truth. He has offered to take responsibility in a pending plea offer. But he still could face trial on charges that include aiding the enemy.

Prosecutors say Manning's motive is irrelevant to whether he leaked the material.