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.

A decree signed by the Russian leader, though long planned, came days after President Biden authorized the use of U.S.-supplied missiles by Ukraine for strikes inside Russia.

MOSCOW, Nov 21 (Reuters) - President Vladimir Putin said on Thursday that the Ukraine war was escalating towards a global conflict after the United States and Britain allowed Ukraine to hit Russia with their weapons, and warned the West that Moscow could strike back.

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.

This week's saber rattling has come during a period in which the war has passed 1,000 days and at a pivotal moment in the conflict between Moscow and Kyiv.