CANBERRA, Australia - Two 16-year-old Australian boys arrested in Sydney after each bought a knife were charged on Thursday with planning a terrorist attack on behalf of the extremist Islamic State group, police said.

The two were arrested by the federal-state Joint Counter-Terrorism Team in the western suburb of Bankstown on Wednesday, New South Wales state Deputy Police Commissioner Catherine Burn said, as Australia marked the 14th anniversary of extremist bombings in Indonesia that killed 202, including 88 Australians.

Burn said police had been concerned about the pair for some time and that the boys had potentially been radicalized by peers.

The pair had bought "two bayonet-type knives" from a Bankstown gun shop then caught a bus to the street near a Muslim prayer hall where they were arrested, Burn said. Police did not know their intended target, but an attack was imminent, she said.

The boys were questioned by police overnight and were charged early Thursday with preparing to commit a terrorist act and with membership of a terrorist organization, namely the Islamic State group.

They faced a potential life sentence if convicted of the planning charge and 10 years for being an Islamic State group member.

The pair were denied bail when they appeared in the Parramatta Children's Court. They did not enter pleas and will remain in custody until their next court appearance on Dec. 7.

State police headquarters in western Sydney was renamed the Curtis Cheng Center two weeks ago in honour of a civilian employee who was fatally shot as he left the building a year ago by a 15-year-old extremist.

"The events of yesterday are extremely sobering for us, particularly given the age of these individuals," Australian Federal Police Deputy Commissioner Michael Phelan told reporters.

"The threat is real, it's enduring, it's still happening and the age of these two individuals is extremely concerning to us," he added.

Federal Justice Minister Michael Keenan said Islamic State recruiters were targeting vulnerable people at younger ages.

"The fact they were 16 is ... an enormous concern to the government and re-enforces the fact we are in a very difficult operating environment where people are radicalizing younger and younger and also radicalizing faster and faster," Keenan told reporters.

Police say the arrests marked the 11th imminent extremist attack that they have prevented in Australia since the terror threat was increased in September 2014. There have been four extremist attacks in Australia in that time.

The bombings on the Indonesian resort Island of Bali on Oct. 12, 2002, were Australia's heaviest loss from an extremist attack.

News from © The Associated Press, 2016