Ottawa will introduce legislation to keep dangerous offenders "on a tighter leash" by lengthening restrictions after their release, Prime Minister Stephen Harper announced Thursday.

The legislation would also make it easier to seek dangerous offender status for criminals convicted of a third violent or sexual crime.

"Next week when Parliament resumes, Canada's new government will table dangerous offender legislation that will deal directly with serious, hardened and repeat offenders," Harper said.

"In a nutshell, we want to impose stricter conditions on repeat offenders to keep such criminals from offending again and again. We will work to ensure that those who are truly dangerous will be put in jail for an indefinite period of time."

The proposed legislation would put the onus on offenders convicted of sexual or violent offences for the third time, to prove they shouldn't be declared a dangerous offender, Harper announced in Toronto.

"We will stop giving criminals the benefit of the doubt," Harper said.

If they are unable to do so, they will face an indeterminate jail sentence with no parole eligibility for seven years.

But Jason Gratl, of the B.C. Civil Liberties Association, argued the justice system should be extremely cautious in how it uses indeterminate sentences.

"We should bear in mind that an indefinite sentence is the nuclear bomb of the sentencing arsenal," he told CTV News.

"We don't have anything more harsh. We don't sentence people to death in this country, and we should be sparing in how we apply our most severe sentences."

The legislation would also put these offenders "on a tighter leash," Harper said, by increasing the maximum duration of peace bonds to 24 months from 12.

"Peace bonds represent a sort of contract between the convicted criminals and the broader community. They lay out acceptable conditions of behaviour for released criminals and put restrictions on that behaviour," he said.

"By putting convicted criminals on a tighter leash after release, we hope to better facilitate their re-integration into the community."

The justice system gives second and third chances, Harper said, adding that this bill will allow the government to draw the line.

Joe Wamback of Canada Crime Victim Foundation, said the announcement was "a start, but not what we were looking for. It's certainly not as tough as we would like to see it be."

University of Ottawa Criminology Professor Irwin Waller agreed that clearly some  legislation is needed to prevent the release of dangerous convicts but he expressed caution.

"My concern is more whether the actual details of the legislation will avoid what has happened in the United States, where these three strikes laws have resulted, yes, in stopping the most violent people from coming out and repeating and repeating and repeating," he told CTV's Canada AM.

"But where very large numbers of other less dangerous offenders have been brought into the system and what happens then is very huge costs to taxpayers.

Waller also expressed his concern that this type of legislation would forego efforts to develop crime prevention policies.

"I'm also concerned that we don't see the challenge of solving the problems of violent crime reduced down to this piece of legislation," he said.

Harper urged opposition parliamentarians to back the proposed legislation bill.

"Frankly, the opposition MPs made a lot of supportive noises about this during the election but it has more often than not been dragging its feet since," he said.

Harper asserted that his government was trying to strike the right balance between defending the rights of individuals and protecting Canadian society.

"We believe that this law respects the charter but we also believe that it is essential for our government to take aggressive action to deal with the most dangerous elements of the criminal population," he said.

On Wednesday, Harper announced the launch of the $591 million Asia Pacific Gateway and Corridor Initiative, saying Canada must serve as a strategic crossroads between the burgeoning economies of Asia, and the United States.

One day earlier, the prime minister promised measurable action on smog and air quality in announcing his government's new environmental program.

The government will table its Clean Air Act when Parliament reconvenes next week, Harper said at a news conference in Vancouver on Tuesday.

With a report by CTV's David Akin