Prime Minister Stephen Harper must explain why "draconian" anti-terrorism measures that were scrapped in 2007 are once again necessary, opposition MPs said Wednesday.

"The prime minister has to explain to us why, if these measures are so important and so necessary, they were not in place for four years. Is the prime minister saying that for the last four, five years, we've been at risk? At greater risk because the measures have not been in place? I think he has to answer that question," interim Liberal leader Bob Rae said.

Rae was reacting to Harper's disclosure in an interview with CBC chief correspondent Peter Mansbridge that his Conservative government plans to bring back two controversial clauses of anti-terrorism legislation that were sunset in 2007.

One allowed police to arrest suspects without a warrant and detain them for three days without charges if police believed a terrorist act may have been committed. The other allowed a judge to compel a witness to testify in secret about past associations or perhaps pending acts under penalty of going to jail if the witness didn't comply. Neither clause was used by police or prosecutors in the five years before they expired.

When asked by Mansbridge if he would try to bring those laws back, Harper replied: "That is our plan."

"We think those measures are necessary. We think they've been useful," he said. "And as you know … they're applied rarely, but there are times where they're needed." An excerpt from the interview was released Tuesday and it will air on The National on Thursday.

The Conservatives put forward a proposal to keep the measures in place for three more years, but the three opposition parties united to defeat the proposal in February 2007 by a 159-124 vote.

Rae said he thinks there are more effective ways to fight homegrown terrorism, which he described as a "real threat," than by re-introducing the legislative measures. Ensuring police and intelligence agencies are co-operating with each other, for example, and integrating people successfully in Canadian society, are more effective ways of combating domestic terror threats, he said.

The interim Liberal leader said police agencies haven't been complaining that their anti-terrorism work has been hampered since the measures were scrapped, nor has Harper made it an issue in recent years.

"The prime minister has to tell us what's changed," said Rae.

The NDP's foreign affairs critic, Paul Dewar, also questioned the prime minister's intentions.

“Stephen Harper's plan to reintroduce these draconian provisions simply isn’t backed up by the facts. The government has produced no evidence to justify this move. Security is obviously important to Canadians, and we can make Canada secure without resorting to measures like these," he told CBC News.

Harper's 'Islamicism' comment draws reaction

There was also reaction to Harper's comment in the interview that Canada is safer than it was on Sept. 11, 2001, but that "the major threat is still Islamicism." His office clarified that Harper was referring to "Islamic terrorism" when he used the term "Islamicism."

Harper cautioned that terrorist threats can "come out of the blue" from a different source, but that terrorism by Islamic radicals is still the top threat, though a "diffuse" one.

Rae said Islam is a religion of peace that has been perverted and twisted, and that Harper should have indicated that in his remarks. The prime minister also should have noted that any religion or ideology can be perverted and used to justify acts of violence, not just Islam, said Rae.

"We don't have to single out just one ... but it would be a little strange to say there hasn't been a perversion of Islam. Of course there's been a terrible perverison of Islam. Whether Islamacist is the right word, I don't know," said Rae.

The NDP reacted to Harper's "Islamicism" remark by accusing him of using "divisive language for political purposes."

“Security is obviously important to Canadians, but we can make our country secure without resorting to divisive politics,” Dewar said in a statement to CBC News.

The prime minister's remarks also prompted reaction, positive and negative, from some members of the Muslim community.

Tarek Fatah of the Canadian Muslim Congress said Islamism is a political doctrine and fascist ideology that encourages violence and seeks the destruction of western civilization and that Harper's comments indicate he understands the difference between it and Islam.

"I'm glad that the prime minister of Canada had the courage to speak out and identify the real enemy," he said.

But Shahina Siddiqui, executive director of Islamic Social Services of Canada, had the opposite reaction and said she was disappointed by the prime minister's comments.

"To take the term Islamic and attach it to terrorism is to point to the entire community, is to brush the entire faith with the same stroke and that to me is not something I expect from a prime minister," she said.