Australia's most-decorated living soldier has been charged over allegations he committed war crimes in Afghanistan.

Ben Roberts-Smith - who left the defence force in 2013 - was arrested at Sydney airport on Tuesday and will face court over five counts of the war crime of murder. He will spend the night in a cell, before a bail hearing on Wednesday.

A defamation judgement in 2023 found the former corporal in Australia's Special Air Service Regiment (SAS) had killed several unarmed Afghans.

The 47-year-old Victoria Cross recipient denies all wrongdoing, and has previously said the allegations against him - which have not yet been assessed at a criminal standard - were "egregious" and "spiteful".

The civil trial was the first time in history any court has examined claims of war crimes by Australian forces.

Roberts-Smith argued the alleged killings occurred legally during combat or did not happen at all, and last year lost an appeal against the Federal Court finding.

At a news conference in Sydney on Tuesday, the Australian Federal Police (AFP) confirmed a 47-year-old former soldier had been arrested and said he would be charged with killing unarmed detainees while serving in Afghanistan between 2009 and 2012.

He faces one charge of the war crime of murder, one of jointly commissioning a murder, and three of aiding, abetting, counselling or procuring a murder.

"It will be alleged the victims were shot by the accused or shot by subordinate members of the ADF [Australian Defence Force] in the presence of, and acting on the orders of, the accused," Commissioner Krissy Barrett said.

In 2020, a landmark investigation known as the Brereton Report found "credible evidence" that elite Australian soldiers unlawfully killed 39 people in Afghanistan, recommending 19 current or former ADF members be investigated.

A specialist team - called the Office of the Special Investigator (OSI) - was set up to do so. It has charged only one other person so far.

Ross Barnett, director of investigations at OSI, said Roberts-Smith's arrest was a "significant step" under "challenging circumstances".

"The OSI has been tasked with investigating literally dozens of murders alleged to have been committed in the middle of a war zone in a country 9,000km from Australia," he said.

"We can't go to that country, we don't have access to the crime scenes... We don't have photographs, site plans, measurements, the recovery of projectiles, blood spatter analysis... We don't have access to the deceased."

Barrett added that allegations of misconduct were confined to "a very small section of our trusted and respected ADF".

"The majority of the ADF do our country proud," she said.

Earlier on Tuesday, Prime Minister Anthony Albanese said he would not comment on the case as it is before the courts.

"[It] is very important that there not be political engagement," he said.

In a statement, the Australian War Memorial has said it will again review its Ben Roberts-Smith exhibit. A plaque accompanying a display of his uniform and medals has been repeatedly updated to reflect the allegations, and the outcome of his defamation case.

At the time Nine newspapers first published reports of the allegations in 2018, Roberts-Smith was considered a national hero, having been awarded Australia's highest military honour for single-handedly overpowering Taliban fighters attacking his SAS platoon.

In a bid to clear his name, he launched a high-profile legal battle - which spanned seven years, cost millions of dollars and was dubbed by some as Australia's "trial of the century".

However a Federal Court judge found - on the balance of probabilities - that Roberts-Smith had taken part in at least four murders, a judgement upheld on appeal.

Anthony Besanko found that Roberts-Smith had twice ordered unarmed men be shot dead to "blood" rookie soldiers, and was involved in the deaths of a handcuffed farmer he kicked off a cliff and a captured Taliban fighter whose prosthetic leg was taken as a trophy and later used by troops as a drinking vessel. (BBC)

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