Former Russian president Dmitry Medvedev said on Thursday that any weapons in Moscow's arsenal, including strategic nuclear weapons, could be used to defend territories incorporated in Russia from Ukraine.
Medvedev, deputy chairman of Russia's Security Council, said that referendums being organised by Russian-installed and separatist authorities in large swathes of Russian-occupied Ukrainian territory will take place, and that "there is no going back":
"The Donbas (Donetsk and Luhansk) republics and other territories will be accepted into Russia."
Medvedev said the protection of all the territories would be significantly strengthened by the Russian armed forces, adding:
"Russia has announced that not only mobilisation capabilities, but also any Russian weapons, including strategic nuclear weapons and weapons based on new principles, could be used for such protection."
The referendums due to take place in the Russian-held parts of Ukraine's Donetsk, Luhansk, Kherson and Zaporizhzhia provinces, as well as part of Mykolaiv province, from Friday are widely expected to produce results overwhelmingly endorsing joining Russia.
The votes, being organised at a few days' notice under military occupation, have been labelled shams by Kyiv and its Western allies.
If formally admitted to the Russian Federation, the occupied territories, where Ukrainian counteroffensives have gathered pace in recent weeks, will under Moscow's nuclear doctrine be entitled to protection from Russian nuclear weapons.
Moscow does not fully control any of the four regions it is expected to try to annex, with only around 60% of Donetsk and 66% of Zaporizhzhia regions held by the Russian army.
Medvedev has regularly issued aggressive statements on the West and Ukraine in recent months, underlining his transformation from apparently Western-minded liberaliser as president from 2008-2012 to strident geopolitical hawk.