The One Nation leader, Pauline Hanson, says she will not “abandon” Ben Roberts-Smith despite his arrest over war crimes, as the Greens declare “no one should be above the law”.

As the prime minister, Anthony Albanese, refused to weigh into Roberts-Smith’s arrest at Sydney airport on Tuesday morning, Hanson reaffirmed her long-held support for Australia’s most decorated living soldier.

“I remain steadfast in my support of Ben Roberts-Smith despite news of his arrest today,” the Queensland senator, whose party is surging in the polls, posted on social media.

“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.”

Roberts-Smith was charged late on Tuesday with five counts of war crime – murder, in relation to three incidents. The maximum penalty for the offence is life imprisonment.

The Victoria Cross recipient was previously accused in a defamation suit of murdering unarmed civilians while serving in the Australian Special Air Service Regiment (SAS) in Afghanistan. He has denied any wrongdoing.

Hanson has been among Roberts-Smith’s political and corporate defenders, along with the mining billionaire Gina Rinehart and media mogul Kerry Stokes.

The former Liberal prime minister Tony Abbott issued a statement of support for the special forces on Tuesday afternoon, which criticised the process that resulted in Roberts-Smith’s arrest.

“Of course, there are rules that have to be observed and enforced, even against soldiers in times of war. Still, it’s wrong to judge the actions of men in mortal combat by the standards of ordinary civilian life,” he said.

“If Ben Roberts-Smith transgressed, why wasn’t this picked up prior to his gallantry awards and why wasn’t any culture of brutality towards prisoners detected by his more senior officers, and dealt with quickly, rather than being allowed to fester, as has been alleged, for over a decade?” he said.

Ross Barnett, the director of investigations at the Office of the Special Investigator, said the five-year investigation faced “a lot of practical challenges”, given the alleged crimes were committed in Afghanistan.

“All of the things that we would normally get at a crime scene. There’s no postmortem. Therefore, there’s no official cause of death. So there are a lot of practical challenges that confront the investigators,” Barnett said.

The Greens defence spokesperson, David Shoebridge, said the arrest was a “moment of accountability and highlights the appalling cost of war on all sides”.

“No one should be above the law,” he said.

“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.”

Shoebridge criticised what he described as a “gaping hole” in the accountability for what happened in Afghanistan, particularly the apparent lack of scrutiny of the role of senior officers who oversaw the deployment of troops to the Middle East.

“Gold braid on your shoulder is not meant to be legal protection from complicity in war crimes,” he said, reiterating calls for a dedicated war crimes investigation unit within the Australian federal police.

Appearing at a press conference shortly after the Nine papers broke news of Roberts-Smith’s arrest, Albanese said he would not comment on the development.

“I have no intention of commenting on a matter that’s clearly before the courts,” he said.

Asked for a second time about the arrest of Roberts-Smith, the prime minister said: “I have no intention of prejudicing a matter that clearly is a legal matter and that’s before the courts and any comment would do so.”

The opposition leader, Angus Taylor, would not comment directly on the arrest but said it “should not detract from the respect we show for our special forces in this country”.

“It is important that we know that our special forces are doing the right thing but the one thing I do know is the vast majority of our special forces do do the right thing and they deserve, as do all our veterans, the respect of our nation,” he said.

A subsequent statement from Taylor and senior Coalition frontbenchers James Paterson, Michael McCormack and Phil Thompson reiterated their “unwavering commitment” to defence personnel and veterans.

“We cannot allow this generation of veterans to be treated like many who returned from Vietnam, left to carry stigma for decades. Today’s charges do not diminish in any way the service of the vast majority of our men and women in uniform,” the joint statement said.