Vladimir Putin, the world's largest nuclear power, has repeatedly warned the West that Russia can respond with nuclear weapons in case of aggression.
Now the question is, what kind of weapons does Russia have and how can the US-led alliance NATO respond to it?
Reuters has reviewed these threats of Putin.
Will Putin use nuclear weapons?
Putin portrays the war in Ukraine as a war for survival between Russia and the West.
According to him, Western powers want to destroy Russia and seize its vast natural resources.
Putin warned the West that he was not just rhetoric when he said he was ready to use nuclear weapons to defend Russia.
Some analysts say that Putin is just making threats, but America is taking Putin seriously.
Russia's claim to 18 percent of Ukraine increases the scope for nuclear threats, as Putin may consider any attack on these areas an attack on Russia.
Russia's policy on nuclear weapons allows for a nuclear attack 'after aggression against the Russian Federation with conventional weapons when the existence of the state is threatened'.
Yuri Fyodorov, a Prague-based military analyst, said that "he (Putin) is just talking rhetoric at the moment."
But what will happen a week or a month from now is difficult to say. Especially when Putin realizes that (conventional) war has not worked.
Is Putin moving towards nuclear attack? On this question, CIA Director William Burns told CBS that "we have to take his kind of threats very seriously because everything is at stake because of him."
However, Burns said US intelligence had no "clear evidence" that Putin would immediately move to use tactical nuclear weapons.
