Australia will indefinitely detain people convicted of "terrorism-related" charges if it feels they pose an ongoing danger to society upon their release, Prime Minister Malcolm Turnbull has said.

Turnbull said the proposed measure was prompted by an increase in the frequency and severity of attacks around the world.

"In the wake of Orlando, Nice, and other terrorist incidents, as well as our own experience ... we cannot afford for a moment to be complacent," Turnbull said in a statement on Monday. 

"This legislation will enable additional periods of imprisonment for terrorist offenders who have served their sentences but are still judged to present an unacceptable risk to the community."

The proposal, to be discussed with state and territory officials who must then pass legislation, is similar to arrangements already in place for sex offenders and extremely violent individuals in some states.

Attorney-General George Brandis said the extension of detention would be a court-supervised process with regular reviews and reassessments.


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"It will of course only apply to individuals who, as they approach the end of a sentence of imprisonment, continue to pose an unacceptably high risk to the community because of their failure to be rehabilitated as a result of a penal sentence," he said.

Under the proposed laws, the age at which children can be held would be lowered from 16 to 14.

Turnbull said the steps were necessary but proportionate.

"They balance the need to keep the community safe with our commitment to privacy and the rights of the individual," Turnbull said, stressing that ultimately it was important the Islamic State of Iraq and the Levant group was defeated. 

A total 44 people have been charged with "terrorism" offences in Australia since 2014, including some involved in the planning of mass attacks on the public, Turnbull said.

Source: Agencies