It will be the first time the remains of an Australian deemed a "foreign fighter" has been repatriated. Under the Foreign Incursions Act, Mr Johnston would have faced 20 years' jail if he had returned alive. The coffin of Australian fighter Ashley Johnston has been returned to Australian soil and authorities are concerned his story could serve as inspiration for others. Fairfax Media understands Department of Foreign Affairs and Trade officials and the Australian Federal Police expressed concern about the transfer. The coffin was delivered by the Kurds directly to representatives of the Johnston family more than three weeks after the 28-year-old was shot and killed in an IS ambush during a battle for control of Tel Hamis in north-east Syria. Security authorities have been in contact with the Johnston family in Canberra, conveying a warning that his actions could be used to recruit other Australians to fight alongside the Kurds but also to stir up antipathy among IS sympathisers in the community.

In a statement, the AFP said it was "extremely concerned by the trend of Australians becoming involved in overseas conflicts". Australian Ashley Johnston was killed fighting the Islamic State. Authorities are particularly concerned by the tag "martyr" given to Mr Johnston, but the Kurdish community say he will be honoured as such regardless. At a recent memorial service in Sydney, attended by 500 Kurdish Australians and Mr Johnston's mother Amanda, posters and flags were displayed honouring him as a martyr. A poster of Mr Johnston, describing him as a martyr.

"No one can stop us," Australian Kurdish Association president Gulfer Olan told Fairfax Media. "He fought over there for humanity, so he is a martyr." She said there was no evidence to suggest that Mr Johnston's personal choice to leave Australia to fight alongside the Kurds – who gave him the name "Heval Bagok" – would encourage others. Kurds from Melbourne, Adelaide and Perth will travel to Sydney for a funeral next week. There will also be a family funeral for Mr Johnston in Canberra. Security expert Greg Barton, a professor at Monash University, said there was a "real danger" that Mr Johnston could be used to recruit Australians and it was a "real dilemma" for authorities. "His mother deserves the liberty to farewell her son and recognise that he was drawn to fight by good impulses. But you don't want others going," he said.

Western recruits might not fully understand who they are fighting for, he said, pointing out that some Kurdish groups have links to the PKK, a Kurdistan Worker's Party (PKK) which has carried out terrorist attacks in Turkey and is deemed a terrorist organisation by the Australian government. The Kurdish People's Protection Units - known as the YPG - has received shipments of weapons carried to the region on board RAAF transport planes. A key recruitment tool for the YPG - a Facebook page called the "Lions of Rojava" - has repeatedly lauded Mr Johnston since his death. A woman called Kader Kandandir, who runs the page, was in contact with Northern Territory Labor president and Senate hopeful Matthew Gardiner before he left his wife and three children to join the Kurds around the same time as Mr Johnston late last year. In a statement, the AFP said: "

Those travelling to Syria or Iraq to participate in the conflict should realise that their actions are illegal. Participation by Australians in the Syrian civil war is against Australian law, irrespective of which side they are fighting for. "The AFP will investigate any allegation of criminality and it would be a matter for the courts to determine." Kurdish Australians have also been circulating to media a letter by Mr Johnston's comrade-in-arms, YPG fighter Renas Berti. In it he compares the Kurds to the Australian Aborigines, saying both had "experienced the cruellest, most brutal and severe form of genocides" and that Mr Johnston had "created a bridge of companionship between Kurdistan and Australia". "From now on, when hearing about Australia, we will not think of a distant continent or even extinct Aborigines. Instead, we will know Australia as a country whose people are willing to speak up for sake of humanity and create sparks in our hearts. And Bagok will always be the first glittering beam of light and hope that reached out to us from Australia.

"He will remain innocent as a lamb, brave as an Aboriginal warrior and a master in war like a Kurdish Guerrilla. This is how we will remember our brave hearted comrade." Loading A memorial fund for Amanda Johnston, established by the Kurdish community, has raised $5600 through 88 individual donations. Follow us on Twitter