Russia may view the use of American missiles, even in a non-nuclear configuration, by Ukraine’s Armed Forces as an element of an attack by a non-nuclear state on russia, supported by a nuclear power. This was stated by Dmitry Peskov, spokesperson for the russian dictator, in response to journalists' questions.
"You can review the relevant paragraphs yourself, but overall, it states that Russia reserves the right to use nuclear weapons in case of aggression with conventional weapons against it that creates a critical threat to its sovereignty or territorial integrity. Aggression against Russia by any non-nuclear state, involving or supported by a nuclear state, is considered a joint attack", - Peskov summarized the doctrine’s provisions.
As previously reported, russia has committed aggression against Ukraine. Russia’s sovereignty and territorial integrity are not under threat. The Western weapons used by Ukraine’s Armed Forces are deployed solely to defend their homeland.