It is understood at least several Australians have crossed into Iraq and have been involved in the bloody fighting concentrated around the north of the country. Iraq conflict: Security authorities are concerned that individuals who left Australia to fight in Syria pose a terrorism threat when they return. Credit:AFP The group, the Islamic State of Iraq and the Levant, has sent shockwaves around Western capitals in the past week by chasing away much larger forces of Iraqi soldiers and seizing swathes of territory including Mosul, the country's second largest city. The Australian Security Intelligence Organisation has previously said it is investigating about 120 to 150 people who have either travelled to Syria to fight or support the extremist rebels from Australia, including some who have been to Syria and come back again. About half of those - or 60 individuals - are believed to be in Syria or the surrounding region. A considerable proportion of those are believed to be with the more extreme rebel groups including ISIL and al-Qaeda affiliate the al-Nusra Front.

At least some of those involved with ISIL are more than just foot soldiers, with some believed to hold more senior positions possibly as commanders, security sources say. "Australians engaging in terrorist activities are not only committing criminal offences, but face risks such as being kidnapped": George Brandis. Credit:Andrew Meares Both ASIO and Attorney-General George Brandis have repeatedly expressed concerns that such people will pose a terrorism threat when they return home battle-hardened and more radicalised. At least 10 Australians are believed to have been killed fighting in Syria with rebel groups. Security officials are also understood to be concerned that ISIL's recent successes against Iraqi forces could be a rallying point and drive further recruitment, including in Australia. There is also a danger that those returning will come back with what a source called ''jihadi street cred'' that could serve as a further recruiting magnet to others.

Senator Brandis said: ''Australians travelling to Iraq or Syria to engage in, or support, terrorist activities are not only committing criminal offences, but may face personal risks such as being kidnapped, seriously injured or killed.'' He said it was illegal for any Australian, including dual citizens, to ''fight, provide funding, provide training, or supply weapons to the conflict in Syria or Iraq''. Most of the fighters are believed to be Lebanese or Turkish dual nationals. Foreign Affairs Minister Julie Bishop said on Thursday that the government was ''deeply concerned'' about dual citizens fighting with opposition groups in Syria and now Iraq and said she had already cancelled ''a number'' of passports. She told ABC radio that some of these fighters, believed to number about 150, had moved from supporting more moderate opposition groups in Syria and Iraq to more extreme groups such as the ''brutal'' ISIL, which espoused a ''virulent form of terrorism''.

''We are concerned that Australians are working with them, they're becoming radicalised, learning the terrorist trade, and if they come back to Australia of course it poses a security threat,'' she said. ''We're doing what we can to identify them. I have cancelled a number of passports on the advice of our intelligence agencies.'' Labor's foreign affairs spokeswoman Tanya Plibersek said on Thursday that Australians returning from fighting in Iraq and Syria was a ''very serious risk'', also pointing to the development of ''street cred'' that could allow returning fighters to ''convince other impressionable young people that going to fight is a good idea''. Andrew Zammit, a researcher at the global terrorism research centre at Monash University, said he had expected Australians would end up in Iraq, given their considerable numbers in Syria, but said it was nonetheless worrying. ''It demonstrates that some of the Australians who joined the Syrian conflict have gone beyond simply wanting to fight the Assad regime, and have very much bought into the broader ambitions and world view of ISIL,'' he said.

''ISIL is a very violent and competent organisation, so there are well-founded fears that some of the Australians fighting with them may return with deadly skills, connections and intentions.'' He said recent murders at a Jewish museum in Brussels, Belgium, allegedly by a man who had fought with ISIL, were an example ''that Australian authorities would be concerned could happen here''. In some cases, the Foreign Minister has cancelled the passports of Australians whom ASIO suspected were poised to travel to Syria to take up weapons. But amid concerns this takes too long and could allow people to board planes before the cancellation can take effect, a report tabled in Parliament on Wednesday urges the government to allow ASIO to go straight to the Immigration Department to suspend a person's passport. The report by the Independent National Security Legislation Monitor, Bret Walker, says passports could be cancelled for up to seven days while investigations are carried out.

Asked whether the passports of those who have gone to fight should be revoked, Ms Plibersek on Thursday said care should be taken when considering such a serious measure. ''But it is important that we take this seriously as a threat and the government is doing that,'' she said, adding that Labor would consider any other measures the government proposed to deal with the issue. Meanwhile, Foreign Minister Julie Bishop has announced Australia will give $5 million in aid to help agencies in Iraq cope with a mounting humanitarian crisis. Asked if Australia should support the regime of Nouri al-Maliki, whose Shia-led government is accused of fanning anti-Sunni sectarian violence in Iraq, Ms Bishop admitted it was ''not a good government''. ''It is the only government in place in Iraq at present,'' she said. ''He's (al-Maliki) now calling for national unity, but that's a start. We need to see a political solution because a military solution could be catastrophic.''

Ms Plibersek on Thursday welcomed the announcement of aid, but said it was a ''drop in the bucket'' given the displacement of one million people. ''I am disappointed about the relatively small amount of aid provided to Syria and I hope that the aid is increased in both cases,'' Ms Plibersek told ABC radio. Loading with AAP Follow us on Twitter