The decision to change Russia's official nuclear doctrine is the Kremlin's answer to a reported decision by the administration of U.S. President Joe Biden to allow Ukraine to fire American long-range missiles deep into Russia.

President Vladimir Putin has 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.

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.