The long-awaited military trial of Bradley Manning got under way here Monday, with prosecutors accusing the US soldier of helping Al-Qaeda by funneling a horde of secret files to WikiLeaks.

The 25-year-old army private faces a possible 154-year jail sentence for his role in the biggest leak of classified information in American history, when a vast cache of information was passed to the whistle-blowing website.

In his first statements at the court martial at a military base outside Washington, Manning confirmed he pleads guilty to 10 charges against him but not the most serious one -- aiding the enemy, chiefly Al-Qaeda -- which could see him spend the rest of his life in prison.

Prosecutors say that from November 2009 until his arrest in May 2010, Manning gave WikiLeaks some 700,000 classified military logs from Iraq and Afghanistan, as well as diplomatic cables from around the world.

Opening the case for the prosecution, Captain Joe Morrow said Manning had passed on information to WikiLeaks despite knowing it would be used by late Al-Qaeda leader Osama Bin Laden and his terror network.

"This is a case of what happens when arrogance meets access to sensitive information," Morrow said.

Morrow said Manning -- who chose a trial before military Judge Denise Lind rather than by jury -- had begun feeding information to WikiLeaks less than two weeks after starting his deployment to Iraq in 2009.

Searches of Manning's computer following his arrest in 2010 proved the soldier was aware of the "consequences of his actions," Morrow added.

"The evidence will show ... the accused knowingly gave intelligence to the enemy," Morrow said. "He knew Al-Qaeda used WikiLeaks," he said, adding that Bin Laden was known to scour classified US reports from Afghanistan.

Morrow said Manning was in regular contact with WikiLeaks founder Julian Assange -- currently holed up in Ecuador's embassy in London as he aims to avoid extradition to Sweden -- to determine the most valuable kinds of information.

He had also provided WikiLeaks with the email addresses of more than 74,000 service members in Iraq, including, names, ranks and positions, Morrow said.

In one period, Manning had "systematically harvested" more than 250,000 US State Department cables subsequently released by WikiLeaks.

"250,000 cables -- that's 25,000 cables a day, more than 1,000 cables an hour," Morrow said.

The court later heard testimony from one of Manning's roommates in Iraq, Eric Baker, who said the young soldier had spent all his spare time on his computer.

Manning's lawyer David Coombs had earlier launched an impassioned defense of the soldier, painting a portrait of someone who had been "young, naive and good-intentioned" who found himself grappling with an internal moral crisis soon after arriving in Iraq.

The then 22-year-old Manning had been traumatized after witnessing a civilian car destroyed in a roadside bombing on Christmas Eve in 2009.

"Everyone was celebrating on this Christmas Eve, everyone but PFC Manning," Coombs said. "He couldn't forget about the lives and the families on this Christmas Eve. At this moment he started struggling."

Manning was a "humanist" who began leaking information out of a desire to "make this world a better place," Coombs added.

It was in this context that Manning leaked a video that showed a US combat helicopter shooting at Iraqi civilians in July 2007. The soldier also transmitted a confidential video of a US air strike on the Afghan village of Granai, where more than 100 civilians lost their lives in May 2009.

"He was a little naive that the information that he selected could make a difference. He released these documents because he was hoping he could help to make this world a better place, he believed this information needed to be released."

He had also leaked information about the military prison in Guantanamo Bay in order to "give a true account of what our nation did" at the facility, Coombs added.

Manning was also battling a "very private struggle with his gender," the lawyer said.

Manning's supporters argue his actions shone a light in the darkest corners of the US-led wars in Iraq and Afghanistan.

But Judge Lind has warned she will not allow Manning's trial to turn into a forum on US foreign policy.

The trial is expected to last 12 weeks. Some evidence will be given behind closed doors for national security reasons.