A secretive and radical program operating inside an Islamic book store in western Sydney is encouraging young Muslims to get involved in Syria's conflict, a 7.30 investigation has revealed.

The bloody conflict in Syria has become a magnet and a new training ground for militants around the world, including Australians.

ASIO has estimated around 100 Australians could be currently fighting in Syria, and four Australians have so far died in the conflict.

Since it opened just over a year ago, the Al Risalah bookstore has gained a reputation as a centre of Islamic extremism.

Key points Four radical sheikhs have preached at the Al Risalah bookstore

Four radical sheikhs have preached at the Al Risalah bookstore The best-known is Bilal Khazal

The best-known is Bilal Khazal Khazal is serving nine years in jail for DIY terrorism book

Khazal is serving nine years in jail for DIY terrorism book Police say they are aware of the sheikhs' activities

Four key sheikhs preaching at Al Risalah

7.30 has been investigating Al Risalah's activities and the people behind it, identifying four key sheikhs.

All are radical, and all are encouraging Australians to get involved in the Syrian crisis.

The most famous of the sheikhs is Abu Suhaib, known to authorities as Bilal Khazal.

Khazal is a former baggage handler for Qantas, trained at a military camp in Afghanistan, and was a confidant of Osama bin Laden.

Belal Khazaal, pictured lecturing at the Al Risalah bookstore.

He was lecturing at Al Risalah in 2012 until he was convicted and sentenced to nine years in jail for producing a do-it-yourself terrorism book.

The possibility that militant sheikhs are radicalising youth at home - before they go to Syria - has Australian authorities on high alert.

Police 'aware' of shop's activities

Community leaders like Jamal Dahoud are concerned about what is taking place.

"The Al Risalah bookstore especially is very secretive, very secret," he said. "They conduct their business in a very secret way. I tried to explore who is behind this group - we can't."

The head of the New South Wales Police counter-terrorism unit told 7.30 they are aware of Al Risalah.

"I am aware of some of activities that go on there and some of the individuals involved," Deputy Commissioner Nick Kaldas said.

He said federal authorities are "very much involved in some of the issues" raised by 7.30.

"It's a matter of us sitting down with our colleagues in the federal sphere and then working out where we go from there, but there has to be tangible evidence and it has to be available to the police," he said.

Deputy Commissioner Kaldas said it is "not advisable" to encourage people to partake in the Syrian war.

"Sending people into a war zone is something that's quite heartless and quite selfish," he said.

"I have to say for someone to be advocating for someone to go and fight in a war but are not prepared to do it themselves tells me something about those who are advocating that."

Government warns fighting in Syria is against the law

Questions have been asked as to whether the Australians who have died in Syria so far were providing humanitarian relief, or if they were also fighting at the front line against the brutal Assad regime.

Their families maintain they weren't fighting and were there to aid the humanitarian effort by helping the maimed and wounded, including women and children caught in the crossfire.

Attorney-General Mark Dreyfus says Australians fighting in Syria could be breaking at least three laws, including the Foreign Incursions Act, which makes it an offence for Australians to participate in this kind of civil war.

Mr Dreyfus also holds concerns that Australians would return from the conflict having been further radicalised.

"Clearly there is a radicalisation that's involved in wanting to participate in this military and violent activity," he said.

"There is a concern before people go, but there is also a concern when they return - as the director-general of ASIO has spoken about.

"If you've gone to Syria, participated in the conflict there - particularly with a terrorist group - and then returned to Australia, it's likely you'll return with terrorist ideology [and] with more knowledge."