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.

Australia has summoned Russia’s ambassador to the country over reports that a Melbourne man was killed after being captured while fighting for Ukraine. Anthony Albanese said on Wednesday that his government was “gravely concerned” about Oscar Jenkins, a 32-year-old teacher, who was captured by Russian forces last year.