Immigration Minister Scott Morrison says he expects there would be bipartisan support for any move to block Australians who have been fighting in Syria from returning to this country.

Spy agency ASIO says about 200 Australians have taken up arms in the Syrian civil war.

Former foreign affairs minister Bob Carr says that while in government, he sought advice on how to block Australian citizens from returning home after fighting in Syria, but was told it could not legally be done.

He has urged the current government to revisit the idea.

Speaking to Sky News, Mr Morrison said the Federal Government was concerned about Australians involved in the Syria conflict returning to "disrupt the significant social cohesion we have in this country".

"We don't want that in Australia, we just don't want it in Australia, and I agree with Senator Carr on that," he said.

"I'm sure there'd be broad-based support across Parliament to ensure that these sorts of things were not imported back into Australia."

Mr Morrison says he would expect bipartisan support in Parliament for any action taken by the Government.

"We are keeping a very close watch on this, a very close watch and I've had consultations before the election where Islamic communities in Australia have raised this with me, in particular about people returning, that they wouldn't want to see a return," he said.

The Labor MP Michael Danby first raised the issue last week.

Australia has 'by far largest number' of Western fighters in Syria

An expert from Melbourne University's School of International Relations says Australians make up "by far the largest" contingent of Western recruits to Syrian armed groups.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 5 minutes 40 seconds 5 m Listen to David Malet's interview with The World Today Download 2.6 MB

Dr David Malet has just published a book about recruits to overseas insurgencies, called Foreign Fighters: Transnational Identity in Civil Conflicts.

He says that while Australians are often involved in overseas conflict, the number in Syria is higher than usual.

"There have been Australians serving as foreign fighters in a number of other conflicts, like Somalia most recently," he told The Word Today.

"But they've never been the largest group of Westerners. So Syria's a little bit unusual. You have just a handful of Canadians and Americans, maybe a hundred or so British and French citizens. But Australia has by far the largest number."

Dr Malet says many Australians are joining the war in Syria because of family ties to the region.

"Australia has an active, politically active Lebanese community which happens to have a lot of local ties to the conflict in Syria," he said.

"It just happens to be that people have relatives, have acquaintances back in home countries who can facilitate getting people across the border into Syria and have connections with some of the militant groups there."

Blocking return could force fighters underground

Dr Malet says Senator Carr's concerns about radicalisation are justified.

"Some security officials from the European Union have looked at the smaller numbers of Europeans who've gone and said not everyone's radical when they go to Syria but most of them probably are when they come back," he said.

"And we've seen some examples of the potential for blowback against Australia before.

"You had four Australians who went to fight in Somalia and wanted to use their skills that they gained there to blow up the Holsworthy Army Barracks.

"So there's certainly the potential and you can understand why any politician would say 'I'm not leaving anything to chance, let's minimise the risk of anybody coming back and committing a terrorist act.'"

But Dr Malet says there would be legal problems with stopping Australian citizens from returning to Australia.

"It's probably not legal. If somebody's a citizen I don't know that you can keep them from returning [to] Australia," he said.

"You could look at stripping them of their citizenship which is what some Arab states have done to foreign fighters.

"But then they're just sort of left floating out there on the global stage and they become a perpetual problem."

Dr Malet says rather than blocking people from returning to Australia, the Government should monitor them after their return.

"Most counter-terrorism operations actually involve just monitoring people until they become an imminent threat," he said.

"So rather than driving people underground, it's probably best just to keep a low profile and watch what they do."

Australian fighters 'could come back home as recruiters'

Dr Malet says Australians who are fighting in Syria at the moment are likely to be some of the most extreme of the fighters in civil conflicts like Syria.

"I think probably the biggest danger is really they come home as recruiters," he said.

"There's a lot of evidence that foreign fighters have gone from places like Iraq and are seen as heroes in their local communities, seen to have credibility to inspire other people to go."

He says by monitoring activities the Government can keep track of recruitment activities in Australia.

"Most people don't simply buy a plane ticket and go off by themselves. They are part of a broader community group, they interact with others online through their mosques and community institutions.

"And that's why I think it's actually probably a safer bet just to keep tabs on people, because they're always talking to someone about how to get involved.

"Then we can monitor, we can get intelligence about who is performing what activities, who is recruiting who, who conduits are for mobilisation and transport. And it's probably better not to drive those sort of conversations underground."