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 has vowed to take decisive measures if harm has been inflicted on Oscar Jenkins, a Melbourne school teacher captured while fighting for Ukraine. Disturbing video footage from December shows Jenkins being interrogated by Russian forces.

There are fears an Australian man captured by Russian forces while fighting for Ukraine has been executed. Oscar Jenkins, a 32-year-old teacher from Melbourne, was reportedly captured in the Donbas region.

Trump has reaffirmed his intention to broker peace in Ukraine, declaring earlier this month that “Putin wants to meet” and that such a meeting is being set up. In the past, he has criticized U.S. military aid for Ukraine and even vowed to end the conflict in a single day if elected.

Russia says it has detected a shift from U.S. President-elect Donald Trump and his team towards recognising the "realities" on the ground in Ukraine, and sees this as a welcome sign as it prepares to study his plan for ending the war.

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Moscow launched more than 40 missiles, and at least 30 were shot down, said Ukraine’s President Volodymyr Zelenskyy, adding about 70 strike drones were involved in the attack. It remains unclear how many were intercepted.

Russia’s military on Tuesday said it would retaliate against Ukraine after Kyiv attacked Russian regions by firing six US-made ATACMS ballistic missiles, six UK-made Storm Shadow cruise missiles and launching one of the biggest drone attacks to date.

Ukraine introduced emergency power cuts in six regions amid what authorities described as a "massive" Russian missile strike, the national grid operator said on Wednesday.