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.

Australia’s Prime Minister Anthony Albanese says his government will take the “strongest action possible” if Russia has harmed an Australian who was taken prisoner while fighting for Ukraine.

Soldiers who served alongside Oscar Jenkins in the Ukrainian armed forces say they are convinced their Australian comrade was killed by Russia's military shortly after being captured last year.