A prominent Russian foreign policy strategist has warned Moscow will 'go nuclear' and leave 'little left' of some European countries if they continue backing Ukraine.

Sergei Karaganov said Russia would initially use conventional weapons, but would resort to nuclear attacks if Europe refused to surrender.

The honorary chairman of Russia's Council for Foreign and Defence Policy also dismissed the prospect of Britain or the United States retaliating with nuclear weapons.

His threats come as Moscow demands European countries cut the military and financial support helping Kyiv resist Russia's full-scale invasion. 

'If they continue this war, a European war with American help, against Russia, on Ukrainian territory, sooner or later we'll feel the need to escalate,' Karaganov told the BBC. 

'According to my scenarios, the first series of blows will be conventional. But if Europe does not surrender, unfortunately, we will have to go nuclear. There will be little left of some European countries.' 

Challenged over the prospect of a European response that would leave nothing of Russia, he insisted there would be no retaliation. 

'No, there will be no response from Europe,' he said. 'What, Britain will attack Russia with nuclear weapons? I hope you're not that crazy. I'm sure the Americans are not that crazy.' 

Karaganov acknowledged that Russia had lost many people during the war, but criticised his government for failing to act harshly enough.

He said Moscow was now stepping up its attacks and destroying Ukraine's ability to function as a viable state.

The remarks come amid mounting tensions between Russia and European countries, which Western officials accuse Moscow of targeting through cyber-attacks, sabotage and drone incursions. 

In Germany, a drone carrying an explosive device was found close to Ukrainian cargo planes at Leipzig airport. 

Western officials believe such incidents form part of an escalating Russian campaign operating in the grey zone between peace and war. 

Russia's foreign minister Sergei Lavrov, meanwhile, accused Europe of waging war against his country when questioned by the BBC about Moscow's alleged hybrid attacks. 

The claim reflects the Kremlin's longstanding portrayal of the conflict as a European war against Russia, despite Moscow having launched the full-scale invasion of Ukraine in 2022.

Putin has given little indication that he is prepared to halt the fighting, despite Russia's heavy battlefield losses and the damage to its economy.

His speeches and statements suggest he remains confident that Moscow can secure a military victory. 

The comments come after Russia on Wednesday warned Nato it was prepared to resort to nuclear weapons if the Western alliance attempted to cut off Kaliningrad, a Russian exclave on the Baltic Sea.

In a document sent to Nato and seen by Reuters, Moscow accused the alliance of a 'dangerous and reckless course' that entailed 'high risks of the outbreak of a direct armed conflict'.

The document said this included the possibility of 'Russian strikes against decision-making centres in the alliance's member states right from the outset.'

'Russia will be ready to use the entire arsenal of forces and capabilities at its disposal, including nuclear weapons, in order to defend its territory should NATO countries undertake any attempt aimed at isolating the Kaliningrad Region from the rest of the country,' the diplomatic note said.

The warning highlighted Moscow's urgent concern at what it has presented as a growing Nato threat to Kaliningrad, a heavily militarised Russian territory that is wedged between Poland and Lithuania and is slightly bigger than the US state of Connecticut.

Nato Secretary General Mark Rutte said the alliance had responded to Russia's message by declaring: 'We are a defensive alliance. And stop the nuclear threats. This is absolutely not called for and not helpful.'

In its written response, seen by Reuters, Nato also said that none of its 'exercises or activities pose a threat to the territory of the Russian Federation'.

'We call upon the Russian Federation to end its unprovoked full-scale invasion of Ukraine. We urge the Russian Federation to refrain from increasingly reckless behaviour towards the Allies and to cease its irresponsible nuclear rhetoric,' it said.