Russian President Vladimir Putin on Tuesday signed a revised nuclear doctrine declaring that a conventional attack on Russia by any nation that is supported by a nuclear power will be considered a joint attack on his country.

Stocks fell and investors fled to safe-haven assets on Tuesday, as global markets reacted to escalating tensions between the world's two largest nuclear powers.

Russian ruler Vladimir Putin issued a decree on 19 November approving Russia's updated nuclear doctrine shortly after the White House allowed Ukraine to use US-supplied weapons to strike deep into Russia.