NATO warned on Wednesday against Russia’s war in Ukraine sliding into a nuclear confrontation between Moscow and the West. Sky’s Mark Stone asked the General Secretary: “Could you outline how NATO defends itself against a nuclear attack? It’s clear that on Russia state media they are openly propagandists, pundits, people close to the Kremlin are not talking in pretty straight and stark terms about a nuclear attack.”

Mr Stoltenberg said: “Russia must stop its nuclear sabre-rattling.

“This is dangerous and it is irresponsible.

“NATO’s there to protect and defend all allies and we convery a very clear message to Russia that a nuclear war cannot be won and should never be fought.

“It just highlights the importance of ending the war in Ukraine because we need to do everything we can to prevent the war from escalating beyond Ukraine and becoming even more deadly and even more dangerous than what we see today.”

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It comes as one of President Vladimir Putin’s closest allies warned the United States on Wednesday that the world could spiral towards a nuclear dystopia if Washington pressed on with what the Kremlin casts as a long-term plot to destroy Russia.

Dmitry Medvedev, who was president from 2008 to 2012 and is now deputy secretary of Russia’s Security Council, said the United States had conspired to destroy Russia as part of an “primitive game” since the 1991 fall of the Soviet Union.

“It means Russia must be humiliated, limited, shattered, divided and destroyed,” Medvedev, 56, said in a 550-word statement.

The views of Medvedev, once considered to be one of the least hawkish members of Putin’s circle, gives an insight into the thinking within the Kremlin as Moscow faces in the biggest confrontation with the West since the 1962 Cuban Missile Crisis.

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Medvedev said the Kremlin would never allow the destruction of Russia, but warned Washington that if it did achieve what he characterised as its destructive aims then the world could face a dystopian crisis that would end in a “big nuclear explosion”.

He also painted a picture of a post-Putin world that would follow the collapse of Russia, which has more nuclear warheads than any other country.

The destruction of the world’s biggest country by area, Medvedev said, could lead to an unstable leadership in Moscow “with a maximum number of nuclear weapons aimed at targets in the United States and Europe.”

Russia’s collapse, he said, would lead to five or six nuclear armed states across the Eurasian landmass run by “freaks, fanatics and radicals”.

“Is this a dystopia or some mad futuristic forecast? Is it Pulp fiction? No,” Medvedev said.