Police say officers had been attempting to assess the counter-terrorism threat level of an individual when he and another man brandished a knife and a tomahawk.
Two men shot by police near the Victoria-NSW border were being assessed by counter-terrorism detectives after converting to Islam.
Officers tried to pull over the brothers, aged 19 and 30, near a camping ground at Barnawartha North about 3pm on Wednesday.
Counter Terrorism Command Assistant Commissioner Ross Guenther told 3AW that counter terror officers were trying to find one of the men to assess if he was a risk.
"It was an intention to go and meet with that person with some of our interstate partners and look at whether we could test their level of radicalisation and any intent to commit an act of violence," he said on Thursday.
However, that meeting never took place and instead the violence erupted.
When the pair were found, they rammed the police car and lunged at the officers with a knife and a tomahawk.
Both were shot by police and taken to Albury Hospital with serious injuries. The 30-year-old was later flown to Melbourne.
They remain in hospital in a critical but stable condition.
The brothers had been in a NSW prison and converted to Islam in that time.
Mr Guenther said he understood they had "very fundamental, very, very rigid" beliefs.
They have a criminal history in NSW, South Australia and Victoria and one of them may have historical associations with outlaw bikie gangs from South Australia, Mr Guenther said.
A Corrective Services NSW spokeswoman said in a statement the pair "were not radicalised while in a NSW prison" but as the matter is for Victoria Police, she would not comment further.
Victorian Premier Daniel Andrews in a statement on Wednesday night thanked "the brave Victoria Police officers who put themselves in harm's way every single day to keep Victorians safe".
There is no ongoing threat to the community.
Detectives are treating the incident as a "violent attack on police members" and not as a terrorist incident.
Homicide Squad detectives will investigate the shooting along with the Professional Standards Command.