Vladimir Putin has been warned his entire army will be "annihilated" if he follows through with nuclear attack threats.
The European Union's foreign policy chief Josep Borrell has hit back at the Russian President's suggestion he could use tactical nukes on Ukraine.
The former Soviet despot chillingly warned last month he wouldn't hesitate to use weapons of mass destruction if his country's territory is threatened.
He told the West "I am not bluffing" but top diplomat Borrell has now retaliated saying "neither" is the EU or NATO, reports the Daily Express.
Putin's national address on September 21 also saw him announce a partial mobilisation of civilians into his armed forces to help turn the tide in his stuttering invasion.
That was followed by the sham annexation of four occupied regions as Russia continues to lose an estimated 500 soldiers a day to death or injury.
Borrell has hit back over Putin's threats, warning him any nuclear attack on Ukraine will see his forces wiped out.
The EU's top diplomat said at the opening of a Diplomatic Academy in Brussels: "Putin is saying he is not bluffing.
"Well, he cannot afford bluffing, and it has to be clear that the people supporting Ukraine and the European Union and the Member States, and the United States and NATO are not bluffing neither.
"Any nuclear attack against Ukraine will create an answer, not a nuclear answer but such a powerful answer from the military side that the Russian Army will be annihilated."
This is the second huge warning directed at Putin in a matter of hours as fears continue to swirl over a possible Russian nuclear attack on Ukraine.
NATO Secretary-General Jens Stoltenberg said the circumstances in which the defence alliance might have to use nuclear weapons are "extremely remote" but warned there would be "severe consequences" if Russia made such a move.
He told a news conference after a meeting of NATO defence ministers: "There would be severe consequences if Russia used nuclear weapons, any kind of nuclear weapon against Ukraine.
"We will not go into exactly how we will respond, but this will fundamentally change the nature of the conflict.
"It means that a very important line has been crossed," added Mr Stoltenberg, referring to the war in Ukraine that followed Russia's invasion of the country.
He made clear the central aim of NATO's nuclear deterrent was to preserve peace and prevent coercion against its allies, and so the circumstances under which it might have to use nuclear weapons were "extremely remote".
On Wednesday, another NATO official warned: "There would be a sharp response - almost certainly drawing a physical response from many allies, and potentially from NATO itself."
The US has also reaffirmed its commitment to defend "every inch" of NATO territory ahead of talks with defence ministers from the alliance that will include closed-door discussions by its Nuclear Planning Group.
US Defence Secretary Lloyd Austin said: "We are committed to defending every inch of NATO's territory - if and when it comes to that."
Earlier today, Alexander Venediktov, the deputy secretary of Russia's Security Council, was quoted by Russian media warning that World War Three could break out if Ukraine were allowed to join NATO.
He is reported to have said: "Kyiv is well aware that such a step would mean a guaranteed escalation to World War Three. The suicidal nature of such a step is understood by NATO members themselves."
Ukrainian President Volodymyr Zelenskiy has already announced a bid for fast-track membership of NATO, but full NATO membership could be some time away as all the defence alliance's 30 members would have to give their consent.
