An Australian who joined Kurds battling the Islamic State group in Syria arrived back home Monday with his parents pleading with authorities not to charge him under foreign fighter laws, calling him "a hero".

Ashley Dyball, 23, was detained in Germany while taking a break from a Kurdish military campaign against IS in northern Syria and deported on Saturday night.

He touched down in Melbourne and was questioned by Federal Police officers for several hours before being allowed to travel on to Brisbane, where he is from.

His lawyer Jessie Smith told reporters in Melbourne he was "interviewed, released without charge pending further enquiry".

Police said any Australian identified as a threat to security would be fully investigated, without specifying whether charges would be laid.

"The public can rest assured that any Australian who is identified as a threat to security will be investigated by the relevant agencies," federal police said in a statement.

"Australians have been consistently warned that by becoming involved in overseas conflict they are putting their own lives in mortal danger," it added.

Australian officials have been increasingly concerned about citizens travelling to Iraq and Syria to join extremist groups such as IS, with some 110 Australians currently fighting in the region. As many as 45 have died.

Canberra has introduced new laws to combat the threat, with foreign incursions offences updated as part of new counter-terrorism laws introduced last year aimed at blocking jihadists going overseas to fight.

Under the laws, it is a crime to fight for militants on either side of the conflict.

- Emotional issue -

Few have left to fight or work against IS, although Dyball is not the first.

Reece Harding, 23, died in June in Syria after stepping on a landmine while battling the militant group alongside Kurdish fighters.

Dyball's father Scott said his son was glad to be home, and criticised the foreign fighter laws.

"How can you have evil and good and say it's the same thing? It's not. It's not the same thing," he told national radio.

"And today it's not just for Ashley, but Harding... And they're heroes in our books. In everyone's books."

He urged the government to grant an amnesty to his son, who travelled to the frontline in May despite government warnings it was an offence to do so.

Immigration Minister Peter Dutton said the government did not want any Australians in Syria or Iraq "however well-intentioned they might be", without saying whether authorities would go easy on Dyball.

"The difficulty is that, my sense, is that this is a very good family. His mum and dad obviously love him very much and it is an emotional issue," he told 2SM commercial radio.

"But we have to recognise that this is a theatre of war and people going off to role play in whatever side that they might see fit, is just not acceptable under Australian law."

Speaking to Australian media from Syria earlier this year, Ashley Dyball said he was carrying out humanitarian work and clearing landmines.