A defamation trial opened Monday pitting one of Australia's most decorated soldiers against three major newspapers that accused him of war crimes in Afghanistan. 

Ben Roberts-Smith, a former member of Australia's elite Special Air Services regiment, is suing the newspapers as well as individual journalists from all three over articles from 2018 that alleged he committed murder and other atrocities while serving in Afghanistan. 

The defendants, including the Sydney Morning Herald, The Canberra Times, and Melbourne's The Age, will argue the reports were truthful, according to court documents. 

Australia's military and police are both investigating numerous war crimes alleged to have been committed by members of elite SAS soldiers in Afghanistan. 

Among the witnesses for the defence are at least four Afghan villagers who are set to appear via video-link from Kabul, court documents show.

Roberts-Smith was awarded the Victoria Cross and the Medal for Gallantry for his service in Afghanistan, among Australia's top military honours. 

He is now an executive for Channel Seven television in Queensland state. 

The Federal Court trial will last for eight to ten weeks, with around 60 witnesses expected to take the stand, a court official said. 

Parts of the trial will likely be closed to the public, including the media, when national security matters emerge. 

Australia deployed 39,000 troops over two decades as part of US and NATO-led operations against the Taliban and militant groups in Afghanistan. 

The country will pull out its small contingent of remaining support personnel by September, in line with the planned US withdrawal.

Last year, an internal investigation into military misconduct found special forces personnel "unlawfully killed" 39 Afghan civilians and prisoners. 

The report was a watershed moment for Australia's government, which had previously attempted to suppress whistleblower reports of the alleged wrongdoing, with police even investigating reporters involved in bringing those accounts to light.