Australian police said Sunday a teenager charged with a terrorist bomb plot was "well advanced" in plans to target a public event, adding they were investigating whether he was radicalized or recruited online.
Tim Cartwright, acting police Chief Commissioner for Victoria state, said officers found "improvised explosive devices" in the boy's family home in the north Melbourne suburb of Greenvale after the 17-year-old was arrested in a raid on Friday.
"We do believe the young man intended to explode the device at an event over the coming days," he said.
"We will allege he was well advanced in preparing a bomb."
Cartwright said it was not yet known if a specific event was targeted. Reports Saturday said Mother's Day celebrations on Sunday may have been the focus of the alleged plans.
Police in the southern state have been searching the house of the boy, whose identity has not been disclosed, before his appearance in a juvenile court on Monday.
Cartwright said investigators were at this stage not looking for anyone else in connection with the alleged plot, but they were exploring the possibility of online radicalization.
"Overseas recruiters and, more broadly, social media are a real challenge for us, a challenge we haven't seen in the past," Cartwright said.
"The Internet provides people the opportunities to radicalize from across the world. It is a real concern for us."
A woman claiming to be the boy's sister told the Sunday Herald Sun he was just a "keyboard warrior", in response to reports her brother was the alleged author of some online comments that sparked concern.
"That's not my brother. He would not hurt a fly," she told the newspaper.
"He is 17. It is just him being a keyboard warrior, it's not a representation of him at all."
The Herald Sun said a friend of the boy told the newspaper he became "very religious, conservative" over the past year.
Two other Melbourne teenagers are facing terror-related charges for allegedly planning an attack on Anzac Day, a event honoring fallen soldiers last month, in a separate police investigation.
Australia raised its threat level to high last September and has since carried out a series of counter-terrorism raids, with alarm fuelled by the departure of more than 100 of its nationals to Iraq and Syria to fight with Islamic State jihadists.
