A Sydney teenager from the same school as the 15-year-old who shot dead a police worker on Friday has been arrested on his way to class.
Police said the boy was asked about alleged social media posts, but became threatening and intimidated officers.
Facebook posts which local media say were written by the boy, who has not been named, defended and praised teen gunman Farhad Jabar's actions.
Jabar was shot dead by police after killing police veteran Curtis Cheng.
New South Wales Police Commissioner Andrew Scipione on Saturday said Jabar's actions were politically motivated and therefore linked to terrorism.
The boy detained on Tuesday was taken away in handcuffs for further questioning at Parramatta Police Station.
He told the Australian Broadcasting Corps that police had taken offence to him filming them on his phone as they patrolled outside the school.
Media reports said he had written posts on Facebook saying the nearby Merryland police station "is next".
The arrest comes as classes resumed for the first time since Friday's shooting, and the end of school holidays.
The NSW Department of Education is offering counselling to Arthur Phillip High School students and staff.
Police accountant Curtis Cheng, 58, was gunned down on the street as he headed home for the long weekend.
Floral tributes were laid for Mr Cheng outside the New South Wales Police Headquarters over the weekend, which is 300m from Arthur Phillip High, by friends, colleagues and even strangers.
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