An estimated 1,710 of the warheads that can be used by the Russian military are deployed on the likes of intercontinental ballistic missiles or at strategic bomber bases, the organization said. The U.S. has approximately 1,670 deployed strategic warheads, according to the FAS.

Russian President Vladimir Putin lowered the threshold for using nuclear weapons, a move that has sparked global concern, after Ukraine's use of US-supplied missiles to strike targets within Russian territory.

Moscow will now consider a conventional attack on Russia by any nation supported by a nuclear power to be a joint attack, according to a change in the country's nuclear doctrine signed into law by Vladimir Putin.