Let police do their job: Keenan

Justice Minister Michael Keenan has called upon Australians to trust law enforcement agencies in their fight against terrorism, saying six attacks have been foiled in the past 12 months alone.

As anti-terrorism authorities grow certain 15-year-old Farhad Khalil Mohammad Jabar did not act alone in murdering police employee Curtis Cheng, Mr Keenan contested allegations police had "dropped the ball" in their monitoring of the situation.

"We do live in a heightened threat environment. We've had three terror attacks in Australia in the past year and our authorities have disrupted a further six," Mr Keenan said to The Today Show.

"We have equipped our authorities with the tools they need to address this.

"People should have confidence that our law enforcement agencies, which are the best in the world, know what they're doing."

Three of the four youths arrested in Wednesday's pre-dawn raids were released from custody on Wednesday night, with some already known to police through last year's Operation Appleby raids.

Mr Keenan said police must be given the space they need to continue their investigations.

"Police are pursuing their lines of inquiry, and they will do so diligently and methodically," he said.

"The most important thing is that anyone involved in this horrendous murder is held to account for their crime."

Mr Keenan admitted a "rather enormous number" of calls are made each day to the National Security Hotline but emphasised these were not solely related to terrorism.