Security crackdown to target 'fanatics'

Tony Abbott says Australians "infected with extremist fanaticism" are being closely watched as he considers a national security crackdown targeting dual nationals.

The prime minister has flagged tougher border protection, immigration and citizenship rules, saying that for too long people who represented a threat to the nation had been given the benefit of the doubt.

About 140 Australians were "openly supporting this Islamist death cult" in the Middle East, Mr Abbott said on Monday.

Authorities have said about 90 Australians have gone to the Middle East to fight, including in Iraq and Syria.

"At least 20 have come back and they're obviously people of great interest to our police and security agencies," Mr Abbott told Kiis FM.

"There is a significant number of Australians who have been infected with this terrible, terrible extremist fanaticism. We are keeping careful watch of them."

It's understood that some are dual citizens.

The prime minister said he wouldn't pre-empt a national security statement he will deliver next Monday.

"But if you look for argument's sake at the history of the Martin Place murderer, at every step of the way, our system gave him the benefit of the doubt," he said.

After the Martin Place siege in December, it emerged that Iranian-born gunman Man Haron Monis was granted a visa in 1996 despite officials in Tehran having warned of his criminal history.

One of two men arrested last week as they were allegedly about to carry out an attack in Sydney - Omar Al-Kutobi - reportedly arrived in Australia in 2009 using another person's passport.

He was given a protection visa before being granted citizenship in 2013.

It's understood that one option being considered by the government is a proposal from Tasmanian federal Liberal MP Andrew Nikolic that Australia follow the lead of countries including Britain, France and Canada, which have moved to suspend or revoke the citizenship rights of dual nationals.

Opposition Leader Bill Shorten was looking for details from the prime minister.

"He has said there is softness in the system, well that's alarming and I think Tony Abbott needs to come clear about where he thinks the softness is," Mr Shorten said.

"We're willing to work constructively in the best interests of our nation's security."

Foreign Minister Julie Bishop, who has the power to revoke the passports of people suspected of involvement in terrorism, said the government was looking at more permanent measures to deal with the terror threat.

"We're now considering what we do when someone's passport has been cancelled, when they're a dual citizen they can be proven to have fought or are fighting with a terrorist organisation overseas, what can we do here in Australia to prevent them being a risk to Australians," she told the Seven Network.

Australian Greens leader Christine Milne said Mr Abbott was "trying to press the terror button, press the fear, anxiety, difference, division button" to shore up his own position.