The 4-year-old document is known as Russia nuclear doctrine and President Vladimir Putin has signed a revamped version lowers the bar on when he could use Moscow’s atomic arsenal, the world's largest.

Russian President Vladimir Putin has formally lowered the threshold for Russia’s use of its nuclear weapons in a revamped version of the country’s

Vladimir Putin on Tuesday signed a decree revising Russia's nuclear doctrine to broaden the basis on which Moscow would consider using nukes, just two days after the U.S. authorized Ukraine to use its longer-range missiles to strike targets in Russia.