Five Australians travelled to fight alongside Russian-backed nationalist militia in Ukraine, according to intelligence provided to the Australian Federal Police, raising concerns the group has been exposed to combat experience that could threaten Australia's national security.

Key points: Five Australians are believed to have travelled to fight in the long-running conflict in Ukraine

Five Australians are believed to have travelled to fight in the long-running conflict in Ukraine The war is increasingly being linked to far-right extremism

The war is increasingly being linked to far-right extremism The government is powerless to stop the men slipping back into Australian society

But the Australian government is powerless to prosecute those who return from the conflict, despite the war increasingly being viewed as inspiring far-right extremists in the same way that fighting in Syria and Iraq influenced Islamic terrorists.

Australian agencies face unprecedented scrutiny about the monitoring of far-right threats in the wake of the Christchurch massacre, amid growing international concern that an informal global network of white extremists is spurring on violence in the West.

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Fighting between Russian separatist and Ukrainian forces in the Donbass region of Eastern Ukraine has claimed about 10,000 lives since the conflict started in 2014.

It is now suspected that at least seven Australians have been involved in the war, which has drawn foreign fighters affiliated with the far-right to both sides of the conflict — Ukrainian and Russian battalions.

Ukraine warns Australia over 'dangerous' returning fighters

Ukrainian officials provided the AFP and Department of Home Affairs with a list of suspected Australian foreign fighters almost six months ago and are strongly pushing for the men to be charged.

Similar approaches to authorities in the United Kingdom and Italy resulted in prosecutions. Those fighters were found to have links to extreme far-right groups in their own countries.

But the AFP is unable to prosecute the Australians, as it is not illegal for them to join the conflict because the federal government ignored a high-level recommendation to make all foreign fighting a criminal offence.

Home Affairs Minister Peter Dutton and AFP Commissioner Andrew Colvin meeting with Ukraine's Minister of Internal Affairs Arsen Avakov and National Police head Serhiy Knyazev in November, 2018. ( Supplied: Minister of Interior of Ukraine )

Ukraine's Minister of Internal Affairs Arsen Avakov and National Police head Serhiy Knyazev met with Home Affairs Minister Peter Dutton and AFP Commissioner Andrew Colvin last October.

"In this conflict there are 'adventurers' from Australia who joined the illegal armed groups," Mr Avakov said in a statement.

"Such kinds of people who have gained experience in hybrid conflicts are also dangerous for your society.

"They are the carriers of specific information which can harm national security … in this area, we cooperate with Italy and the UK, so we would like to provide you this list of five Australian citizens for response and tough actions."

Ukrainian authorities would not reveal the identity of the Australians, the information they had regarding their involvement with Russian-backed separatists, or whether they had all returned to Australia.

Conflict zone a finishing school for far-right fighters

Sorry, this video has expired The Australian former soldier turned Neo-Nazi who fought in Ukraine

The ABC has previously reported that former Australian Defence Force personnel, including some with ties to far-right groups, fought with Ukrainian battalions in the same war.

The conflict is increasingly being linked to far-right extremist attacks across the globe.

In some cases, extremists used the conflict almost as a finishing school, while others allegedly met with senior figures involved in the Ukraine conflict before committing violence, or expressed an affiliation with those fighting in Ukraine.

In 2017, two Swedish neo-Nazis from the country's notorious Nordic Resistance Movement bombed a centre for asylum seekers after reportedly training with Russian battalions who fought in Ukraine.

A Ukrainian scout watches over a strip of no man's land between Ukrainian government positions and those held by the Donetsk People's Republic. ( ABC: Bryce Wilson )

In an indictment released last year, the FBI alleged that three American white supremacists from the Rise Above Movement met with members of the Ukrainian neo-Nazi battalion Azov during a trip to Europe to celebrate Hitler's birthday.

One of the American men has been charged with a series of assaults on protesters, including during the Unite the Right rally in Charlottesville, where a woman was killed.

Tarrant's links to Ukraine being investigated

Accused Christchurch gunman Brenton Tarrant also touched on Ukraine prior to last month's attack on two mosques which killed 50 people.

In a manifesto published online shortly before the massacre, Tarrant alluded to visiting Ukraine during travels which shaped his world view.

The Black Sun used in Azov Battalion's logo was among the many white supremacist symbols and names that painted on equipment Tarrant allegedly used in the shooting.

Ukrainian authorities would not comment on whether they had established if Tarrant, an Australian citizen, had travelled there.

But they confirmed Tarrant did not apply for a visa before leaving Australia.

They said that if it was found he had been in Ukraine, he must have obtained a visa from another embassy abroad, or entered through the militarised zone, leaving open the possibility that he fought in the conflict.

"The Ukrainian Ministry of Internal Affairs is assisting in investigating the circumstances surrounding the terrorist act," a spokeswoman said in a statement.

Tarrant is believed to have travelled through eastern Europe in 2016 and 2018 and other countries in the region, including Bulgaria and Romania, have confirmed he visited.

Mystery surrounds five returned fighters

Azov recruits in training in southern Ukraine. ( Supplied: Vladimir Cheppel )

The suspected involvement of Australians in the Ukrainian conflict demonstrates the growing complexity of monitoring the threat of extremists, according to Bellingcat online investigator and author Robert Evans.

Fighters from across the world have been drawn to the conflict, in some cases because of their connection to nationalist and far-right groups in their home countries, or because they are attracted by slickly-produced propaganda which compares with films released by Islamic State.

Mr Evans has travelled to Ukraine to report on the conflict and is an expert on fascist movements.

"I would definitely be very concerned," he said.

"I would expect law enforcement in Australia to be looking closely at these guys."

A Ukrainian position looks over the rebel Donetsk People's Republic territory only 50 metres away. ( ABC: Bryce Wilson )

There are clear connections between some people affiliated with Ukrainian and Russian forces and established ultra-nationalist and far-right groups in Australia.

Sydney man Simeon Boikov, the leader of pro-Kremlin group the Zabaikal Cossack Society of Australia, has clashed repeatedly with Ukrainians in Australia and overseas.

He confirmed that his travel to eastern Ukraine led to him being questioned by NSW joint counter-terrorism team police, but denied being involved in the conflict.

Sydney man Simeon Boikov in Ukraine, where he denies he was involved in any conflict. ( Supplied )

He suspects Ukrainian security agencies included him on the recent list of five Australians who should be investigated for fighting with Russian separatists, as they believe he is a terrorist.

The ABC has confirmed Mr Boikov has spent time with Russian battalions in eastern Ukraine, and is understood to have met with several separatists who were the subject of Australian government sanctions after the downing of flight MH17.

Mr Boikov denied he fought in the conflict, but said it would be difficult to prove anyone had been involved, even if it became a criminal offence, because of the nature of the battle.

Mr Boikov has attended multiple rallies and meetings with Australia First Party leader Jim Saleam, who is considered one of Australia's foremost white supremacists.

At a 2016 rally in Sydney which commemorated the killing of the Russian ambassador to Turkey, the pair were joined by Nathan Sykes, an alleged neo-Nazi troll; Iggy Gavrilidis, a representative of Golden Dawn, the Greek nationalist party; and members of the Night Wolves, a pro-Putin motorbike club which is subject to sanctions or banned in several countries.

Mr Boikov said these individuals and the groups they represented were attracted to Russia because of the perception that the country supported nationalism, despite its history of defeating fascism and Nazis.

He said Russia's strong stance against Islamic extremists may have also attracted the groups, which are anti-Muslim, particularly in the context of immigration.

Fears of an escalation in violence' from right-wing groups

Ethan Tilling behind the Right Wing Resistance flag at a Reclaim Australia rally in November 2015. ( AAP: Dan Peled )

Australians who fought with Ukrainian militia groups have also been associated with the far right.

One of these men, Ethan Tilling, is a former member of Right Wing Resistance, a trans-Tasman white supremacist group. He says he is no longer affiliated with the far right.

Another former member of RWR became one of the first right-wing extremists placed under an extended supervision order in Australia because a court found he was at high risk of committing a terrorist act.

Ricky White, who was second-in-charge of the NSW chapter of RWR, was found by the NSW Supreme Court in December to pose "an unacceptable risk of committing a serious terrorism offence... consistent with his previously held white supremacist views."

White burned down a church in 2016, made threats to people associated with a Jewish museum in 2014, and was associated with right-wing extremist groups, skinhead culture and Odinism, the court found.

Right Wing Resistance members have international connections and could be capable of an act of terrorism, according to academic Paul Spoonley.

Australian man, Ethan Tilling, on the Donbass frontline in 2017. ( Supplied: Andriy Tsaplienko )

Professor Spoonley is a pro-vice chancellor at Massey University in Auckland and has closely watched RWR since it was founded in New Zealand about a decade ago.

He provided an expert report in the Ricky White case, revealing the group expanded to Australia in 2011.

"They are very much in the tradition of white supremacist and nationalist movements in ideology and activities, and their imagery is very aligned with contemporary neo-Nazi groups," Professor Spoonley told the ABC.

"There is the potential for an escalation in violence from these groups — they do threaten that they will act against their 'enemies' — and they tend to mandate individual acts of violence [by] those who are sympathetic to their views."

Ethan Tilling joined the Georgia National Legion and fought with Ukrainian nationalists against pro-Russian separatists. ( Snapchat )

The ABC understands Queensland joint counter-terrorism team officers questioned Ethan Tilling on his return from the Ukraine and he was deemed to not pose a threat to national security, but the government would not confirm if a similar approach would be taken to other Australians involved in the conflict.

Mr Tilling told the ABC he did not know Mr White or Brenton Tarrant, and said he did not know if the alleged Christchurch gunman fought in Ukraine.

"It was a six-month period in my life, I only ever knew five other people in the right-wing scene.

"I didn't go [to Ukraine] for any political reason. It had nothing to do with politics, I was going there because women and children were being killed."

In 2014, Australia's watchdog on national security laws, Bret Walker SC, recommended to Federal Parliament that foreign fighter laws should be changed, so that all foreign fighting would be illegal unless approved by the government.

Mr Walker, the former Independent National Security Legislation Monitor, told the ABC last year in the wake of revelations Australians had fought in Ukraine that his recommendation was largely ignored.

"Those are people whose skills, experiences and lack of sensitivity are very likely to constitute dangers in this country," he said at the time.

"There is a domestic concern, not just a concern about Australia's obligations in relation to prohibiting war, but also domestic concern in terms of terrorist dangers in Australia."

The AFP and Mr Dutton's office declined to comment.