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.

The stakes have never been higher in the Ukraine-Russia war. In the week that saw the conflict pass its 1000th day, Western powers substantially boosted Ukraine's military arsenal - and the Kremlin made its loudest threats yet of a nuclear strike.

It began with a peace move nobody wanted and ended with an experimental missile strike so rare in war Moscow gave a 30-minute heads-up to Washington.