A series of major flaws have been exposed in national security laws stripping terrorists of Australian citizenship.

Key points: Australia's Independent National Security Legislation Monitor questions possible loopholes created by the citizenship laws

Australia's Independent National Security Legislation Monitor questions possible loopholes created by the citizenship laws Home Affairs officials suggest if there is confusion about a person's citizenship when an offence occurred, the minister may step in

Home Affairs officials suggest if there is confusion about a person's citizenship when an offence occurred, the minister may step in Authorities believe there are around 80 to 100 Australian, or ex-Australian, foreign fighters still in the Middle East

The Federal Government urgently passed the laws in 2015, targeting dual citizens heading to the Middle East as foreign fighters for the Islamic State group.

But a review by an independent watchdog has uncovered that, in some circumstances, the laws could make it harder to prosecute terrorism offences and gather intelligence.

Automatic loss of Australian citizenship "doesn't pass muster", according to the Independent National Security Legislation Monitor (INSLM), James Renwick SC.

He raised his concerns in a public hearing in Canberra into the 2015 changes to the Australian Citizenship Act.

"Some criminal offences require one to be, for example, an Australian citizen and it may be that there is an unintended effect that loss of citizenship means that you can't prosecute such people for those offences," he said.

Dr Renwick pointed specifically to another of the Federal Government's recent national security laws that make it an offence for an Australian to enter a "declared area" in a foreign country controlled by terrorists.

But for dual citizens, their Australian citizenship is automatically revoked when they engage in terrorism-related activities, raising the prospect of a legal loophole, as entering a declared area is only an offence for Australian citizens.

Sorry, this video has expired Home Affairs Minister Peter Dutton spoke about the laws late last year.

Under questioning, Australian Federal Police Deputy Commissioner Leanne Close conceded there were difficulties with the two laws.

"At the instant they cross the line, assuming they had the terrorist intent … then and there, what happens?" Dr Renwick asked.

"Do they lose citizenship first? Do they commit the offence first?

"Let's assume they commit the offence and then immediately after that lose the citizenship. Unless you exempted them [re-instated citizenship], you couldn't then prosecute them either at all or in a way which fully reflected their criminality, could you?"

Deputy Commissioner Close replied: "You're right, Dr Renwick. It is complex."

When Home Affairs Department officials were asked how such a scenario would be handled, it was suggested the Home Affairs Minister would have to reinstate the person's Australian citizenship to pursue the prosecution and then seek to use other laws to once again revoke their citizenship after that.

Automatic removal of citizenship could cause confusion

Dr Renwick also raised concerns about the loss of citizenship for terrorism-related offences being automatic, rather than a decision by the Home Affairs Minister or a court.

Someone could lose their Australian citizenship and not know about it, or authorities may pursue someone not knowing whether they are still a citizen.

"It seems to me to be unsatisfactory that the Government can't tell at a particular time that a person has or hasn't ceased to be a citizen," Dr Renwick said.

Authorities confirmed that since 2015 about a dozen dual citizens have had their Australian citizenship automatically revoked under the laws, the most high-profile being Melbourne-born Islamic State member Neil Prakash.

Linda Geddes admitted it could be hard to determine a person's citizenship status at the time of an offence. ( AAP: Rohan Thomson )

Dr Renwick quizzed the Home Affairs Department's Counter-Terrorism Coordinator, Linda Geddes, about the uncertainty, suggesting it raised complications in criminal prosecutions.

Renwick: "It's simply not possible to say there have only been 12 people affected by these laws." Geddes: "There is that possibility, yes." … Renwick: "You may not know, perhaps until years later, whether a person has lost citizenship and equally it may be hard to say they lost citizenship at this point in time. You agree with that, don't you?" Geddes: "Yes, that's right."

Evidence put to the INSLM hearings also pointed to complications for intelligence agencies charged with gathering information about potential terrorist acts.

Intelligence agencies have restrictions on whether they can spy on Australian citizens or foreign citizens, so if someone's citizenship status is unclear, it creates legal confusion.

Ms Geddes confirmed it was causing practical problems for Australia and its 'Five-Eyes' intelligence partners (the United States, United Kingdom, Canada and New Zealand).

Authorities believe there are about 80 to 100 Australian, or ex-Australian, foreign fighters still in the Middle East.

Arrest warrants have been issued for 39 since Islamic State's control of territory in Iraq and Syria collapsed.

Dr Renwick will deliver his review to Attorney-General Christian Porter in August.