Prime Minister Malcolm Turnbull has warned the threat of terror attacks has grown and there is a serious need to beef up Australia's counter-terrorism laws.

Key points: New laws allow for convicted terrorists to be kept in jail once their sentences have finished

New laws allow for convicted terrorists to be kept in jail once their sentences have finished Period of time extended on sentence is up for negotiation with states and territories, Attorney-General says

Period of time extended on sentence is up for negotiation with states and territories, Attorney-General says Opposition will consider legislation on its merits, Mark Dreyfus says

The Commonwealth has called on state and territory governments to introduce new laws allowing for convicted terrorists to be kept in jail once their sentences have finished, with periodic reviews of the risk a prisoner could pose if released back into the community.

Mr Turnbull said he believed the plan would have overwhelming support around the country.

"In the wake of Orlando, Nice and other terrorist incidents — as well as our own experience since September 2014, resulting in the charging of 44 persons — we cannot for a moment be complacent," Mr Turnbull said.

"We are as agile as our opponents, we are determined to ensure that as they develop new ways of threatening us, we are able to respond quickly and effectively."

The Prime Minister said the proposal was still being refined.

"[The proposed laws] balance the need to keep the community safe with our commitment to privacy and the rights of the individual," he said.

"They follow a direction I gave last week to the counter-terrorism coordinator Greg Moriarty for advice on the implications of the lone attacker terrorists such as those we saw recently, particularly in Nice earlier this month.

"Together the measures we are announcing today are designed to deter terrorism, prevent it, ensure that the nation and our people are kept safe and to provide reassurance that Australians can and should continue going about their daily lives and enjoying their freedom in the usual way."

Extended detentions will be subject to reviews, appeals: Brandis

Attorney-General George Brandis said there would be a number of safeguards in place.

"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," Senator Brandis said.

"This will be a court-supervised process, it will be a process informed by medical and psychological assessment and details about patterns of behaviour while in custody, participation or willingness to participate in rehabilitation programs while in custody.

"In the event that a court-supervised process makes an order extending a period of detention, there will be periodic review of that and the offender can seek leave to apply to the court during the currency of any period of extended detention for review of that determination."

He said the exact period of time a convicted terrorist would have their sentence extended by was up for negotiation with the states and territories.

"The phrase 'indefinite detention' has been used frequently, including by me — perhaps it's best to think about this as extended detention — so that a period of detention per sentence may be extended for a defined period," Senator Brandis said.

The Attorney-General said there would be annual reporting to Parliament on the number of orders granted, and the scheme would be reviewed after a number of years.

Malcolm Turnbull and George Brandis say the laws would 'deter terrorism'. ( AAP: Dan Himbrechts )

Shadow attorney-general Mark Dreyfus said the legislation would need strict checks and balances before the Opposition would consider supporting the legislation.

"I'm encouraged by the approach taken by the Government so far on proposed national post-sentence detention legislation," Mr Dreyfus said.

"It's likely to be a controversial measure in many quarters and a careful approach is necessary, in particular I note the Government's insistence that post-sentence detention orders would be made the subject of court review and of course also subject to periodic review as the Prime Minister made clear this morning."

Extended detentions preferable to life sentences: expert

George Williams, an anti-terror legislation expert and Dean of Law at the University of New South Wales, has previously said a post-sentencing detention scheme for convicted terrorists should only apply in the most exceptional of cases.

"I'm always reluctant to go down the path of these type of measures, but I think on this occasion this can be justified if it's done in the right way, and the detail really does matter," Professor Williams told AM.

"If we have people who can be shown to continue to pose a demonstrable risk, if it is determined by a judge not by a minister, if there's also periodic review, and if it only applies to offenders who have already been convicted of very serious crimes, then yes, I think it can be justified.

"I think it's preferable to have a scheme of this kind in place, rather than the alternative which would be simply having much, much longer sentences — potentially life sentences for these people, without the prospect of release."

He said the reason the Commonwealth was reaching out to the states and territories for their support was because of previous legal precedents set in the High Court, when convicted sex offender Robert Fardon challenged his ongoing detention.

"The Queensland scheme for high-risk sex offenders was valid, but what the Court also indicated is that it might not be valid if it was passed by the Federal Parliament, that perhaps this could only be a state scheme," Professor Williams said.

"That's the reason why we're seeing the Commonwealth not deciding to go it alone, they're negotiating with the states and territories.

"They would like to insulate themselves from that legal risk by having it set up at the level that the High Court has said can support these type of regimes."

Professor Williams said there were people currently in Australia's prisons that could be subject to the new proposal.

"We now have a long experience of people being jailed for terrorism, going back several years, and we've seen an accelerated charging of people - this now has become a routine part of the legal system, unfortunately," he said.

"The Government is facing this issue of what should happen when these people are released, certainly it will face a political question as to whether it's doing enough to prevent that and to protect the community.

"Even though I think a scheme here can be justified, it's got to get the balance right — we've got to make sure that these people are only detained when there is a clear and present danger."

Proposal a 'distraction' from the real solutions

New South Wales Council of Civil Liberties president Stephen Blanks said he believed the announcement was being used as a distraction to stop the community talking about real solutions for combating the risk of terrorism.

"People who have been convicted of serious terrorism offences are in jail for many years to come, we're not being told who is about to be released that they're concerned about." Mr Blanks said.

"With the sex offender cases, there were particular individuals that we were told were about to be released that represented a danger.

"We're not being given that information now.

"I don't think there's anybody about to be released, this is possibly just window dressing."