The girlfriend of accused war criminal Ben Roberts-Smith has branded a prominent Liberal MP a “traitor” after he posted about attending an Anzac Day ­service.

Sarah Matulin wrote “yeah you’re a traitor” on an Instagram post by Andrew Hastie.

The former SAS captain posted it on Saturday, writing that “honouring our veterans and ADF” was “a responsibility for all Australians, young and old”.

“Lest we forget,” he wrote to accompany a photo of himself with his young children at an Anzac Day event in Perth.

Hastie was an SAS captain in Afghanistan. He also gave evidence in Victoria Cross-holder Roberts-Smith’s defamation trial against the Nine newspapers, corroborating evidence from other soldiers.

Roberts-Smith now faces five charges of war crime murder and Hastie is a potential witness in his criminal trial. Roberts-Smith, who is on bail, denies all allegations.

Matulin’s comment, first reported by the Nine newspapers, was deleted. On Monday, in a statement through Roberts-Smith’s lawyer Karen Espiner, she acknowledged making it.

“It was a mistake to make that comment in a public forum and wasn’t done with Ben’s knowledge,” Matulin said.

Also among the comments on Hastie’s post was one from former Liberal staffer Bruce Lehrmann. He was found by a Federal Court judge, on the balance of probabilities, to have raped fellow staffer Brittany Higgins in Parliament House.

“Your betrayal of BRS and the ADF won’t be forgotten, hope it was worth it for ministerial promotion,” Lehrmann wrote.

Supporters of Ben Roberts-Smith marched in Melbourne on Sunday. Photo: AAP

On Sunday, protesters shut down city streets in Melbourne to decry the “injustice” of Australia’s most decorated living soldier being charged with multiple war crimes.

Waltzing Matilda and the national anthem blared on the steps of Victorian Parliament House on Sunday as about 150 people gathered, flying Australian flags and red ensigns.

Attendees at the rally, which was organised by the far-right National Workers Alliance, turned out to show their support for Roberts-Smith and other SAS members under investigation for alleged Afghanistan war crimes.

Some wore war medals, while others carried banners and placards that proclaimed Roberts-Smith a “warrior not criminal”.

Roberts-Smith had earlier distanced himself from the rally.

“Mr Roberts-Smith and his family are not in any way involved in this rally, nor associated with its organisers, and have not been consulted by the group in question,” a spokesperson said.

Roberts-Smith attended an Anzac Day commemoration on the Gold Coast on Saturday, speaking with supporters.

“Today is bigger than me,” he told The Australian. “This is a day … about remembering every single person that has given us the country that we live in.”

In Melbourne, National Workers Alliance leader Matt Trihey told the crowd that “what has happened is an absolute injustice”, as attendees called for charges against Roberts-Smith to be withdrawn. 

“We are here for the veterans who are having their legacy, their honour and their integrity questioned by what is an illegitimate government that is acting against the will of the people,” he said.

The National Workers Alliance’s publicly stated goals include a moratorium on all immigration and the “preservation of Western culture and identity”.

A small group of counter-protesters opposed the group, separated by two lines of police.

Brandishing their own banners, the group attempted to shout down the rally with chants of “always was, always will be Aboriginal land” and “Nazi scum off the street”.

The Roberts-Smith supporters then took to the streets, shutting down busy corridors and blocking trams. One marcher was seen yellow at people dining outside, telling them to “go back to where you came from”.

A spokesperson for the former SAS soldier said he and his family were not in any way connected to the Melbourne rally.

-with AAP