Jens Stoltenberg, secretary general of NATO has issued a warning and stated that any usage of nuclear weapons from Russia's end will meet grave consequences.
In an interview with NBC, Stoltenberg said that any deliberate attack on NATO's critical infrastructure will be met with a firm and united response.
"Putin's nuclear rhetoric is dangerous, reckless," said Stoltenberg.
The secretary general made it clear that the best way to respond to Russia's proclaimed annexation is by giving more and more support to Ukraine.
Talking about Ukraine's possible membership in NATO, Stoltenberg said that it should be agreed by all allies which comprise 30 member states.
Earlier, former UK RAF Airmarshall, director general of joint force development and director general of the Ministry of Defence Edward Stringer said that Russia is most likely to use nuclear weapons as its army falters in Ukraine.
Springer added that Putin's forces have failed at multiple points, and it is one factor which may compel Putin to make use of deadly nukes in the country's arsenal.
"What the Americans are trying to do there is avoid the situation where the collapse of the Russian forces is so dramatic and consequential that Putin now feels that he cannot defend Mother Russia," Springer told Daily Star.
He added: "It is fair to say that the way the war develops, the more frightened Putin feels, then, the more he himself may do something reckless."
He further noted that Putin may even use the nuclear weapon to shock the west, thus opening up a chance to negotiate.