The US army was overwhelmed when WikiLeaks published more than 700,000 secret diplomatic and war documents handed over by soldier Bradley Manning, a retired officer testified in the sentencing phase of the convicted private's court-martial.

"The ones that hit us in the face were the Iraq logs," retired Brigadier General Robert Carr said in a Forte Meade, Maryland court on Wednesday, a day after a military judge found Manning guilty of 19 charges over the leaks in 2010, the biggest breach of classified data in US history.

"No one had ever had to deal with this number of documents," Carr said.

A prosecutor told the sentencing hearing that the leaks caused military intelligence officials to rethink how much access to allow low level intelligence analysts like Manning. 

Judge Colonel Denise Lind began hearing arguments on Wednesday on how long a sentence he should face, with the soldier's lawyers expected to argue for leniency.

While Manning, 25, was acquitted on the most serious charge of aiding the enemy, sparing him life without parole, he could still face decades in a military prison.

Manning faces a maximum penalty of 136 years in prison.

After the verdict was announced on Tuesday, experts assessed Manning's legal recourse.

"This case is going to be reviewed automatically, and will likely be in the appeals process for several years," Yale military law professor Eugene Fidell told Al Jazeera.

Manning "would have a very good appellate argument if convicted of aiding the enemy," he said, adding that he "wouldn’t speculate, for the time being, on what [Manning's] arguments would be".

The American Civil Liberties Union called Tuesday's decision a gesture to scare future whistleblowers.

"Since Manning already pleaded guilty to charges of leaking information – which carry significant punishment – it seems clear that the government was seeking to intimidate anyone who might consider revealing valuable information in the future," the ACLU said in a statement emailed to Al Jazeera.

'Dangerous precedent'

Meanwhile, Julian Assange, whose WikiLeaks organisation revealed Manning's data dump to the world, reacted negatively to the verdict.

"It is a dangerous precedent and an example of national security extremism," he told reporters at the Ecuadorean Embassy in London, which is sheltering him. "This has never been a fair trial."

Judge Lind's verdict follows about two months of testimony and evidence. Manning, a 25-year-old native of Oklahoma, admitted to sending more than 470,000 Iraq and Afghanistan battlefield reports, 250,000 State Department diplomatic cables and other material, including several battlefield video clips, to WikiLeaks while in Iraq in early 2010. WikiLeaks published most of the material online.

The video elements included footage of a 2007 US Apache helicopter attack in Baghdad that killed at least nine men, including a Reuters news photographer and his driver.

The WikiLeaks case is by far the most voluminous release of classified material in US history.

Manning said he sent the material to expose war crimes and deceitful foreign policy and that he didn't believe the information he handed over would harm troops in Afghanistan and Iraq or threaten national security.

Source: Al Jazeera and agencies