The Wikileaks disclosures
strained US-Afghan relations, a retired US Army general said at the
sentencing hearing of Pte First Class Bradley Manning.
Brig Gen Robert Carr said documents Pte Manning leaked named hundreds of friendly Afghan villagers, putting their lives at risk.Pte Manning faces up to 136 years in prison after his conviction for espionage and 19 other charges.
He had admitted passing hundreds of thousands of documents to Wikileaks.
On the first day of the sentencing hearing in a military court in Fort Meade, Maryland, the prosecution sought to demonstrate the extent of damage caused by the 2010 leaks.
That issue is at the heart of the sentencing process, and also in the wider debate over whether to treat Pte Manning as an ethical whistle-blower or a traitor, says the BBC's security correspondent Gordon Corera.
On Tuesday, a military judge convicted Pte Manning of 20 out of 22 counts, including espionage and theft of government data.
Julian Assange, founder of the Wikileaks anti-secrecy organisation, has condemned the verdict and called for it to be overturned.
'Friendly Afghans at risk'
Gen Carr, an intelligence expert who led a Pentagon task force investigating the damage done by the leaks, testified that protecting the Afghan population was one of the US military's primary missions.
"We had to get close to the population, had to understand that population, and we had to protect them," he told Judge Col Denise Lind on Wednesday.
"If the adversary had more clarity as to which people in the village were collaborating with the US forces, then there is a chance that those folks could be at greater risk."
The general testified that US relationships with other countries suffered as a result of the leaks. He said some of the exposed diplomatic cables were "very blunt" and made it harder to communicate with other nations.
But Gen Carr acknowledged that no-one named in the Afghan war logs was killed.
He said the Taliban tied a killing for which it claimed responsibility to the WikiLeaks disclosures, but he acknowledged the victim's name did not appear in the leaked files.
More than 20 witnesses are expected to be called for the sentencing hearing, which could take weeks.
Analysts say Pte Manning, who did not testify in his defence, could still take the stand during the sentencing phase.
Pte Manning's defence lawyer is expected to argue the soldier never intended to harm US national security, an argument made at length and with apparent success during the trial, as he was acquitted of the most serious charge against him, aiding the enemy.
'Bloodlust' During the trial the judge stopped both sides from presenting evidence about whether the leaks had endangered national security or US troops in Afghanistan and Iraq, but the prosecution and defence will be able to bring that up at the sentencing hearing.
The judge also limited evidence of Pte Manning's motives. At a pre-trial hearing, he testified that he had leaked the material to expose the "bloodlust" of US forces and the country's diplomatic deceitfulness. He did not believe his actions would harm the country, he said.
Among the items Pte Manning sent to Wikileaks was graphic footage of an Apache helicopter attack in 2007 that killed a dozen people in the Iraqi capital Baghdad, including a Reuters photographer.
The documents also included 470,000 Iraq and Afghanistan battlefield reports and 250,000 secure state department cables between Washington and embassies around the world.
Pte Manning, an intelligence analyst, was arrested in Iraq in May 2010. He spent weeks in a cell at Camp Arifjan, a US Army installation in Kuwait, before being transferred to the US.