Victoria Chief Commissioner Ken Lay has warned of increased tensions with the Islamic community and warned police to exercise extreme caution after the shooting of an 18-year-old suspected of being a threat to national security.

The teenager was shot and killed by police on Tuesday night after allegedly stabbing two members of the counter-terrorism task force. Both police were taken to hospital in a stable condition.

“I think there will be raised tensions, there’s no doubt about that,” Mr Lay said a press conference on Wednesday morning.

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“I have written to all members of police advising them to exercise extreme caution.”

“We need to be prepared for anything.”

Both Mr Lay and AFP acting commissioner Andrew Colvin confirmed the man had been known to police for several months.

Mr Colvin described the man as “a person of interest for national security reasons” and confirmed his passport was cancelled last week.

“There were a range of factors which gave us concern about his intentions,” Mr Colvin said.

“Factors in terms of activity at shopping centres, more about rhetoric and things that he had been heard to say.”

Mr Lay confirmed the man, who is of Afghani decent, had been seen at a shopping centre brandishing an ISIS flag.

Mr Colvin said the investigation would be turning to associates of the deceased teenager.

“Now we will have a closer look at this gentleman and who his associates are. We’re at the start of an investigation here,” Mr Colvin said.