The US Army was overwhelmed when WikiLeaks published more than 700,000 secret diplomatic and war documents handed over by soldier Bradley Manning, his court martial has been told.

Retired Brigadier General Robert Carr told the hearing, which has found Private Manning guilty of 19 charges over the biggest release of classified data in the country's history, that the logs on the Iraq War were the "ones that hit us in the face."

Judge Colonel Denise Lind began hearing the arguments yesterday on how long the soldier should face in jail, with the soldier's lawyers expected to argue for leniency.

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

The soldier was in Baghdad in 2010 when he was arrested and charged with leaking files including videos of a 2007 attack by an American Apache helicopter gunship in Baghdad that killed a dozen people, including two Reuters news staff, diplomatic cables and secret details on prisoners held at Guantanamo Bay.

Manning's attorneys were expected to argue that the Army private was not trying to jeopardise national security. He did not testify during his trial or during the first day of his sentencing hearing.

A prosecutor, Major Ashden Fein, said Private Manning's leaks "impacted the entire system" for granting defence analysts access to classified information.

Some observers said the case of Private Manning, as well as that of former CIA security contractor Edward Snowden, illustrated the risk in granting security clearance so broadly.

Snowden last month released to media documents detailing US programmes to monitor phone and internet usage.

In a court martial that stretched over two months, military prosecutors argued Private Manning betrayed his country when he handed over files to the anti-secrecy WikiLeaks website. The US government said the breach put national security at risk.

Observers said the verdict could have "a chilling effect" on ­WikiLeaks by making potential sources of documents in the United States more wary about handing over secret information.

It could also encourage the US to seek to prosecute WikiLeaks founder Julian Assange for his role in ­publishing the information.

Mr Assange has been in the Ecuadorean embassy in London for over a year to avoid extradition to Sweden, where two women have accused him of sexual assault. He says he fears Sweden might hand him over to the US.

Private Manning faces ­spending the rest of his life in prison despite being cleared of helping al Qaeda in its fight against the US.

It had been argued that the mastermind of the 9/11 terror attacks, Osama bin Laden, used the leaked documents to devise plots against the country.