One Nation leader Pauline Hanson has led a furious online backlash over the arrest of Australia's most decorated soldier over alleged war crimes in Afghanistan.

Ben Roberts-Smith, 47, was taken into custody by Australian Federal Police officers at Sydney Domestic Airport after arriving on a flight from Brisbane on Tuesday morning, reportedly in front of his teenage twin daughters.

The Victoria Cross recipient will face court later on Tuesday after he was charged with five counts of war crime-murder, following a joint investigation between the Office of the Special Investigator (OSI) and the AFP.

The maximum penalty for the offence of war crime–murder is life imprisonment.

Hanson vowed to stand by Roberts-Smith in the wake of his arrest as she slammed authorities over the huge cost to reach this stage.

'I remain steadfast in my support,' the senator posted online.

'Ben, his immediate and broader defence family need the Australian people's support right now and I will not abandon him like so many other politicians.

'AFP and OSI have spent $300million over 10 years to get to this point.'

Controversial political activist Drew Pavlou was also quick to leap to Roberts-Smith's defence.

He pointed out that Roberts-Smith was awarded the Victoria Cross for  singlehandedly storming two Taliban machine gun positions by himself in order to save his SAS team. 

'And this is how we repay him,' Pavlou wrote.

'Tell me: When does the Taliban plan on holding war crimes tribunals into their own people?'

But not everyone agreed with the backlash.

Greens senator David Shoebridge shared a screenshot of an article about the arrests and simply wrote: 'Good.' 

He later issued a press release praising the arrest. 

'This is a moment of accountability and highlights the appalling cost of war on all sides,' Shoebridge said. 

'No one should be above the law. These charges relate to killings that happened in Afghanistan between 2009 and 2012, for victims and survivors that is far too long to wait for justice.

'Deployments of troops in overseas conflicts always come at enormous cost to people on the ground who face the horror and brutality of war.

'It is essential we remember the human cost of war right now as the US and Israeli attacks on Iran and the Iranian people escalate.

'Gold braid on your shoulder is not meant to be legal protection from complicity in war crimes.

'If justice is to be fully delivered there must be further and closer attention paid to the role of senior officers who directed and oversaw Australia's deployment in Afghanistan.'

Prime Minister Anthony Albanese repeatedly refused to weigh in on the case during a press conference on Tuesday. 

'I have no intention of commenting on a matter that's clearly before the courts,' he told reporters.

'That is a matter that is very important that there not be political engagement in what is a matter that is now the subject of legal proceedings, so I don't intend to comment.'

AFP Commissioner Krissy Barrett confirmed a 47-year-old had been charged with five counts of war crime - murder during a press conference outside the AFP Sydney Headquarters on Tuesday afternoon.

She refused to refer to Roberts-Smith by name under the AFP's usual practice.

'It will be alleged the man was a member of the ADF when he was involved in the deaths of Afghan nationals between 2009 and 2012, in circumstances that constitute war crimes under the Commonwealth criminal code,' Commissioner Barrett said.

'It will be alleged the victims were detained, unarmed, and were under the control of the ADF members when they were killed.

'It will be alleged the victims were shot by the accused or shot by subordinate members of the ADF in the presence of and acting on the orders of the accused.'

She said the alleged victims were not taking part in hostilities at the time of their alleged murder in the war zone. 

The Office of the Special Investigator, comprised of 54 investigators, launched an investigation into the soldier in 2021, with about a dozen other war crimes investigations into ADF personnel in Afghanistan ongoing.

'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 9000 kilometres from Australia,' OSI director Ross Barnett said.

'Because we can't go to that country.... we don't have access to the crime scenes... we don't have access to the deceased, there's no post-mortem... so it's a very challenging starting point for all these investigations.'

In 2018, Roberts-Smith sued Nine newspapers and journalists Nick McKenzie and Chris Masters for defamation after they reported he had committed war crimes in Afghanistan.

In 2023, the Federal Court's Justice Anthony Besanko found the claims that Roberts-Smith was responsible for the murder of four unarmed male civilians were substantially true, on the balance of probabilities.

McKenzie and Masters were first to report details of Roberts-Smith's arrest on Tuesday morning.

Roberts-Smith appealed against Justice Besanko's decision to the Full Court of the Federal Court but lost. He was refused leave to further appeal to the High Court.