Russian 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 on his country.

Russian President Vladimir Putin on Tuesday lowered the threshold for nuclear weapons use, just two days after the U.S. authorized Ukraine to use long-range missiles inside of Russia. Putin

Putin lowered the bar for a nuclear attack after the US lifted a ban on Ukraine using long-range missiles. Ukraine carried out its first strike with the weapons.