(Bloomberg) -- European leaders said Friday that US President Joe Biden’s warning about “Armageddon” and Russia’s possible use of nuclear weapons shows the seriousness of the threat from Moscow’s escalation in Ukraine.

Estonian Prime Minister Kaja Kallas told reporters Friday that his nuclear threats should be taken very seriously. “If nuclear weapons are used, then this is a whole new level,” she said. “And nobody can win a nuclear war. This is very clear. And I understand those messages have been given to Putin and the Kremlin that you can’t win this war.”

In recent days, US and other western officials have downplayed the imminent risk of a nuclear weapon being used, saying there were no indications that Moscow is preparing to use its arsenal. Russian President Vladimir Putin has renewed his nuclear threats as he announced the annexation of Ukrainian territory, but the rhetoric echoes similar warnings he has issued since he invaded Ukraine in February.

European Union leaders, meeting in Prague to discuss the war in Ukraine and the bloc’s energy crisis, were joined Friday via videoconference by Ukrainian President Volodymyr Zelenskiy.

Biden’s statement Thursday that even the use of small tactical nuclear weapons could lead to “Armageddon” suggests that Washington is worried that Putin could shift tactics as he continues to suffer embarrassing setbacks in Ukraine.  

Biden Says Putin Threats Real, Could Spark Nuclear ‘Armageddon’

With Russian troops steadily losing ground to a Ukrainian counteroffensive, Putin has called up 300,000 reservists and vowed to use “all the means at our disposal” to defend his country, including the occupied parts of Ukraine that he recently annexed. 

The Russian president hasn’t explicitly said that means nuclear weapons, but some of his lieutenants have called for employing tactical ones to send a signal of the Kremlin’s resolve. The smaller tactical ones would likely take some time to get ready and in position for deployment.

In Putin’s Nuclear Brinksmanship, Weapons Leave Room For Warning

“We’re trying to figure out what is Putin’s off-ramp? Where does he get off? Where does he find a way out?” Biden said at a fundraiser in New York City. “Where does he find himself in a position that he does not, not only lose face but lose significant power in Russia?”

EU leaders have remained united in support of Ukraine, even as Putin’s threats have unsettled member nations, particularly in the east. 

“We really need to think there is a kernel of reason still left, that we will avoid nuclear war,” said Croatian Prime Minister Andrej Plenkovic.

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