The federal government's proposal would see those convicted of terror offences locked up even after their sentence has expired, should they still pose a high risk to the community.

The Commonwealth would rely heavily on state governments for such a model, and has reached out to the ACT government to legislate post-sentence detention in support.

But the ACT, along with Victoria, is put in a unique position due to its human rights laws.

To be passed through the ACT Legislative Assembly, any form of indefinite detention would need to comply with the territory's Human Rights Act, which experts say is a difficult, but far from impossible proposition.

At this stage, the ACT government has not committed either way. It reserved its position on pre-charge and post-sentence detention at the last Council of Australian Governments meeting in April.

Mr Corbell says he wants to see more evidence that the new laws are justified and a proportionate response to the threat.

"Proposals for indefinite detention raise fundamental concerns about the rule of law in a democratic society," Mr Corbell said. "The ACT shares concerns raised by the Law Council of Australia and others in relation to these proposals."

Attorney-General George Brandis is expected to meet his state and territory counterparts again this week, and the government is seeking to move swiftly on the plan in the wake of the attacks in Nice and Orlando.

The Coalition's plan is aimed at high-risk terror detainees, and would hold them as a preventative safety measure.

They would be allowed normal appeal rights, and would have their cases regularly reviewed. Their extended detention would be supervised by the courts.

University of New South Wales law expert Professor George Williams said the ACT's human rights laws did not necessarily preclude the introduction of a limited form of indefinite detention.

"It could be [compatible]. It's all about justifications," he said. "For example, if it was just indefinite detention, then the answer would be 'no'."

"If, on the other hand, it's detention which is subject to regular ongoing reviews to assess whether continuing detention is justified, it's different."

He said the ACT's human rights laws would effectively force a balance between addressing the terror threat and safeguarding individual rights.

"That's exactly what that legislation is designed to do," he said.

Mr Turnbull wrote to state and territory leaders recently asking for their support on Sunday.

Having state governments enact post-sentence detention terror laws would help protect the scheme from High Court challenge.

Mr Corbell said the ACT would examine closely the "rationale for and the scope of these proposals".

"The ACT government supports in principle measures that reduce the threat of terrorism and terrorist acts but any new scheme, such as a post-sentence detention scheme, which impacts on a person's rights and liberties must be a proportionate response to a demonstrated need," Mr Corbell said.

Professor Williams, who is broadly supportive of the terror laws, said Mr Corbell's cautious approach was the right one.

But he said the Commonwealth may only really need the support of states, and could potentially legislate separately from the ACT.

"The Commonwealth's largest problems are in the states," he said. "It may still have a problem in the ACT, it's not clear. The constitutional waters are murky there."