Ukrainian President Zelensky claims that Russia is planning to attack Ukraine with a nuclear weapon. At the same time, Russian state TV claims that World War Three has already begun.
Whether or not Russia really will fire a nuke is suspect, however what is becoming more and more obvious is that the war between Russia and Ukraine is really a war between Russia and NATO. After all most of the weapons Ukraine is fighting with have been supplied by NATO. There are thousands of foreign nationals already on the ground in Ukraine- fighting on the behalf of the Ukrainian people.
For Russia, the involvement of NATO and foreign nationals makes the Ukrainian war a world war and a war whose outcome could be disastrous and an existential to Russia.
With the scope of the war changing and Russia prepared to fight until the end, anything is possible.