A naval base, military barracks and a court complex were allegedly among the targets of the Sydney teenager charged with an alleged terrorist attack.

Tamim Khaja,18, arrested in the Sydney suburb of Parramatta on Monday in a car park where be believed he was meeting with a gun dealer, had reportedly been on police radar since 2015.

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It is alleged Khaja planned to use a semi-automatic weapon to commit the attack, and that he had scoped out Garden Island Navy Base, Victoria Barracks and Parramatta Court Complex as possible location sites.

Counter-terrorism investigators believed the attack was “probably imminent”, according to the ABC.

Khaja allegedly tried to travel to Syria in February to join Islamic State, but was stopped at the airport as his passport had been cancelled.

The teen did not apply for bail, or appear in court on Wednesday and has remained in custody.

His lawyer Osman Samin declined to talk to waiting reporters about the case, only saying that the presumption of innocence should be maintained despite the media attention.

“I seek to proceed on that footing and I urge the public to do so as well, otherwise I can’t make any further comments,” he said.

Khaja was first brought to the attention of police in 2015, when a tip off was made to the National Security Hotline.

It is believed he used to hold extremist Islamic prayer sessions at his Epping Boys High School, and may have been linked to Operation Appleby terror suspect Maywand Osman and convicted extremist Milad Al Ahmadzai, who also attended the school.