And the message from one of Australia's top former diplomats is blunt: "So be it".

The federal government this month committed $70m in "lethal and non-lethal" support to Ukraine, as it defends itself against an unprovoked Russian invasion.

But the presence of far-right paramilitary groups on both sides of the conflict has sparked fears Australia could inadvertently arm extremists.

Former Defence secretary Dennis Richardson on Wednesday accepted Australia could not control where its weapons end up, but said the short-term priority is neutering Mr Putin's "unprovoked and blatant aggression" in Ukraine.

Mr Richardson said future governments would be responsible for managing the fallout.

"Bad things might happen down the track as a result of the arms that are now flowing into Ukraine ... [but] that is something that will need to be addressed if and when the time comes," he told the National Press Club.

"If there is a risk that down the track that arms might fall into the wrong hands, then so be it."

Ukrainian President Volodymyr Zelensky has created a foreign legion and urged foreigners to travel and take up arms, something Prime Minister Scott Morrison warned could be a legally-fraught "suicide mission".

Ukraine's head of mission in Australia Volodymyr Shalkivskyi confirmed Australians have expressed an interest in travelling to the warzone, but was not clear on whether any had.

But the invasion has also energised far-right groups, raising the prospect some travelling intend to bolster extremist groups already active in the region.

President Zelensky's Jewish heritage is a particular fixation for many pro-Russian extremists. But others have expressed an interest in fighting against Moscow, some citing the presence of Muslim Chechens in Russian forces.

American intelligence believes Kremlin-linked mercenary force the Wagner Group has been dispatched to eastern Ukraine, having also fought in Syria.

Prominent members have been pictured wearing Nazi uniforms, and the group was reportedly named after Adolf Hitler's favourite composer. Its alleged owner, oligarch Yevgeny Prigozhin, is closely tied to Mr Putin and has been hit by western sanctions since the invasion.

But Australia's weapons funding for Ukraine is particularly complicated by the fact the Azov Battalion, a neo-Nazi paramilitary wing, has been folded into Ukraine's official armed forces.

Members of the group, linked to war crimes by the United Nations, regularly wear neo-Nazi insignia - including on Ukrainian military uniforms. A video posted by official Ukrainian military accounts appeared to show Azov fighters using pig fat to grease bullets meant for Muslim Chechen troops deployed in Russia.

Asked whether the federal government had taken any steps to avoid arming Azov, a Defence Department spokesperson declined to answer directly.

"Australia's contribution of military assistance is provided to defend Ukrainian sovereignty against Russia's unprovoked, unjust and illegal war," they said.

"The assistance has been provided under a formal, international legal instrument with the Government of Ukraine."

Former US Secretary of State Hillary Clinton has cited Afghanistan, where an insurgency fighting Soviet forces with western arms went on to form al-Qaeda, as a potential model for Ukraine.

Thousands of foreign fighters also descended on Syria during the country's bloody civil war, sparking alarm over the prospect of battle-hardened extremists returning to their home countries to commit atrocities.

That threat was laid bare by the 2015 Paris terror attacks, killing 137, carried out by an Islamic State cell with tactical experience in Syria.

Foreign fighters have been present in eastern Ukraine since the 2014 annexation of Crimea.

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Katja Theodorakis, head of the Australian Strategic Policy Institute's counter-terrorism program, said Syria was "instructive" to the situation in Ukraine but warned against wholesale comparisons.

Australians were barred from travelling to Syria, but Ms Theodorakis said fighters heading to Ukraine are more likely to be framed as freedom fighters than security or terror threats.

"That's a pretty big turn-around, and has policy implications," she said.

"We should be really concerned about getting the nuances around this right. It's problematic how Ukraine seems to have become a proxy for the free world.

"Joining a war is a radicalising experience that comes with many long-term consequences."