Kremlin figures indicated that the expected annexations would heighten the prospect of Nato being drawn into the conflict if it did not accept Russian territorial gains.
Dmitry Medvedev, the deputy chairman of Russia’s security council, said: “Encroachment onto Russian territory is a crime which allows you to use all the forces of self-defence.
“This is why these referendums are so feared in Kyiv and the West. They would completely change the vector of Russia’s development for decades. And not just of our country – the geopolitical transformation of the world would be irreversible once the new territories were incorporated into Russia.”
Margarita Simonyan, the influential head of the RT state television network, said: “Judging by what is happening and still about to happen, this week marks the eve of our imminent victory of a nuclear war. I can’t see any other option.”
Washington has so far said weapons it has supplied to Ukraine should not be used to fire on Russian territory. However, that does not extend to unlawfully annexed territory such as Crimea, which Russia seized in 2014.
Tatyana Stanovaya, a Russia analyst at R.Politik, said: “[This] is an absolutely clear ultimatum from Russia to Ukraine and the West – either Ukraine retreats or there will be a nuclear war.
“In order to secure a victory, Putin is ready to hold the referendums immediately in order to get the right, as he sees it, to use nuclear weapons to defend Russian territory.”
Ukrainian officials said Kyiv’s counter-offensive would continue even if Russia formally annexed new areas.
Dmytro Kuleba, the foreign minister, said: “Sham ‘referendums’ will not change anything. Russia has been and remains an aggressor illegally occupying parts of Ukrainian land. Ukraine has every right to liberate its territories, and will keep liberating them whatever Russia has to say.”