Australia's former foreign minister on Monday urged the government to consider barring Australians who fight in Syria from returning home.

Security officials fear Australians are being radicalized through fighting in Syria and will heighten the terrorism threat in Australia.

Bob Carr was foreign minister until the former Labor Party government lost power in an election last month. He told the Australian Broadcasting Corp that as minister, he had been advised by his department that preventing Australians from returning from the Syrian civil war would be illegal because it would leave them stateless.

Carr urged the new government to seek a legal option.

"Australians are right to be apprehensive about people whose fighting skills have been honed there who seek to return to Australia full of murderous ideological bent," Carr told ABC.

"We should continue to explore whether blocking the return of people is remotely available to us as an option," he added.

Attorney General George Brandis said in a statement his government "is seriously concerned that Australians are fighting in Syria", including some with Jabhat al-Nusra, which is a listed terrorist organization under Australian law.

"Any potential investigations of Australians involved in the Syrian conflict would be a matter for law enforcement agencies," the statement said.

Shandon Harris-Hogan, an expert on radicalization in Australia and a researcher with Monash University's Global Terrorism Research Center, said an unprecedented 80 Australians are involved in the Syrian fighting. Some sources put the figure as high as 200.

No more than a dozen Australians had been involved in each of the previous Middle Eastern and Central Asian conflicts in recent years.

Harris-Hogan said only about 10 veterans had returned to Australia from the Syrian conflict and none had been charged.

It is illegal under Australian law for any Australian - including dual citizens - to fight, provide funding, provide training, or supply weapons to either side of the conflict.

"The bulk of the problem is very much yet to impact us," Harris-Hogan said of the threat of returning veterans of Syria.

"It will be a year or two down the track when you potentially have 50, 60, 70 of these guys returning - if the conflict was to end and the protracted nature of how it looks at the moment means that probably won't happen anytime soon," he added.

AP