Australia has vowed it will take the “strongest action possible” if Russia has harmed one of its nationals captured fighting for Ukraine, after reports emerged the prisoner of war may have been killed.

Oscar Jenkins, an Australian teacher fighting for Ukraine, was reportedly captured and interrogated by Russian soldiers. His status and whereabouts are unknown.

Australian Prime Minister Anthony Albanese promised the "strongest action possible" if reports of an Australian national being executed by Russian forces while fighting for Ukraine are verified, CNN reports.

Australia has promised retribution if reports Russia killed a prisoner of war are confirmed as the federal government faces a call to expel the ambassador.