Final day of referendum in Russian-held areas of Ukraine

Russian men cross the border at Verkhny Lars between Georgia and Russia on Tuesday (Zurab Tsertsvadze/AP)

The final day of voting was taking place in Russian-held regions of Ukraine on Tuesday, in a referendum that is expected to serve as a pretext for their annexation by Moscow but which has been rejected as a sham by Kyiv and its western allies.

As the vote was nearing its end, a senior Kremlin official issued the bluntest warning yet that Russia is prepared to use nuclear weapons to halt a Ukrainian push to reclaim Russia-occupied areas.