Russian President Vladimir Putin on Tuesday lowered the threshold for a nuclear strike in response to a broader range of conventional attacks, and Moscow said Ukraine had struck deep inside Russia with U.S.-made ATACMS missiles.
Putin approved the change days after two U.S. officials and a source familiar with the decision said on Sunday that U.S. President Joe Biden's administration allowed Ukraine to use U.S.-made weapons to strike deep into Russia.
https://www.reuters.com/world/europe/putin-issues-warning-us-with-new-nuclear-doctrine-2024-11-19/