Vladimir Putin threatened to strike Nato countries with nuclear weapons if they send troops to Ukraine.
The Russian president said soldiers deployed to Kyiv could provoke a nuclear war and the “destruction of civilisation”.
Addressing the Kremlin in his annual state of the nation speech, he also boasted that Russian troops were advancing “in a number of areas” across the front line in Ukraine as Kyiv runs low on shells and critical equipment.
His nuclear threats come after Emmanuel Macron, the French president, said he would not rule out Nato putting boots on the ground, sparking controversy and division within the alliance.
Mr Macron had said Nato should do “everything needed so Russia cannot win the war”.
Putin used his speech, which comes just weeks away from the presidential election, to tell Kyiv’s allies that Russian “strategic nuclear forces” are “in a state of full readiness for guaranteed use”.
“They should eventually realise that we also have weapons that can hit targets on their territory,” he continued.
“Everything that the West comes up with creates the real threat of a conflict with the use of nuclear weapons, and thus the destruction of civilisation.”
Putin has made various nuclear threats in the past but has cooled his rhetoric in recent months. After his speech he was accused of “nuclear sabre-rattling” in a bid to discourage Ukraine’s allies from deepening their involvement in the war as Kyiv struggles with ammunition shortages while Moscow presses home its advantage.
Russia has made a number of key gains in the war, taking the key city of Avdiivka earlier this month.
Its troops are recently thought to have entered the village of Robotyne in the south – one of a handful of hard-won gains from Ukraine’s counter-offensive last summer.
‘We should not be spooked by Moscow’
Tobias Ellwood, a senior MP who sits on the defence select committee, said: “Putin’s latest nuclear sabre-rattling is an attempt to leverage visible discord within the West about how support for Ukraine progresses.
“We should not be spooked by Moscow and remain totally committed to pushing Russian forces out of Ukraine,” he told The Telegraph.
However, it comes after leaked Russian military files showed Putin’s forces had rehearsed using tactical nuclear weapons against major world powers – including its ally China.
The classified papers, first reported by the Financial Times, showed the criteria for a nuclear response is lower than it has ever publicly admitted. This includes an enemy incursion on Russian territory and 20 per cent of its ballistic missile submarines being destroyed.
Last week Putin took a widely publicised flight in a nuclear Tu-160M bomber in what was perceived as another implicit threat to the West about Russia’s nuclear capabilities.
Elsewhere in his speech on Thursday, he claimed Nato was attempting to expand eastwards and that Russia must not repeat its mistakes of the Cold War.
