Putin is the primary decision-maker on the use of Russia's nuclear arsenal. The doctrine said any attack by a non-nuclear power supported by a nuclear power would be considered a joint attack, and that any attack by one member of a military bloc would be considered an attack by the entire alliance, it said.

Russian President Vladimir Putin formally lowered the threshold for his country's use of nuclear weapons Tuesday, after the U.S. allowed Ukraine to strike inside Russia using American missiles.

Putin's goals in Ukraine remain the same: weakening Ukraine's ties to NATO, hindering Ukrainian nationalism and territorial gains.