Putin nuclear threat is desperation, says EU commission

"This is also yet another sign of his desperation with how his aggression is going against Ukraine," he said.

Putin had earlier on Wednesday announced the "partial mobilisation" of some 300,000 Russian citizens to fight in Ukraine.

The new mobilisation of more Russian troops has put Lithuania's rapid reaction force on high alert, while Latvia said it would not offer refuge to any Russians fleeing Moscow's call to arms.

The move comes as Ukraine regains large swatches of territory previously seized by Russia.

The Russian president had also raised the prospect of nuclear arms, noting that Russia is ready "to use all weapons resources at our disposal".

The country is estimated to have almost 6,000 nuclear warheads. Of those some 1,500 have been retired or are set to be dismantled, leaving behind an arsenal of around 4,500.

But the European Commission said any such use would have "unforeseen consequences for the entire world".

Jamie Shea, a former Nato official, now teaching at University of Exeter in UK, said western leaders need to respond in a calm and measured way in public, but that behind the scenes Nato allies also need to consult on what they can do to dissuade Russia "from going down this reckless path."

"The use of a nuclear weapon is highly unlikely but its use would be so potentially catastrophic that no stone can be left unturned in preventing it from happening," he said.

Similar remarks were made among western heads of state and government.

Among them was Dutch prime minister Mark Rutte who described Putin's speech as a kind of panic reaction. "Russia cannot win this war," he said.

Others are calling for Putin and his foreign minister to personally face justice for their "aggression" against Ukraine.

Putin's pre-recorded speech, which was broadcasted on state TV, follows other plans to launch referenda in Ukraine's eastern Donbas in a bid to fold the region into Russia.

But Stano would not say if the EU would impose further sanctions on Russia should the referenda in the self-proclaimed People's Republics of Luhansk (LPR) and Donetsk (DPR) take place.

Instead he said such topics, and others, are currently being discussed among EU states at the United Nations Generally Assembly in New York.

"Whatever the outcome of this sham, illegal referendum would be, these regions will be still legally part of Ukraine," he said.

Those views were also shared by German chancellor Olaf Scholz, who told the UN assembly in New York that Putin's war in Ukraine was an act of "imperialism plain and simple."

France's president Emmanuel Macron, also at the UN, had also accused Russia of imperialism.

"Who is a hegemon now if not Russia?", he said.

Meanwhile, Putin's defence minister, Sergei Shoigu, said that Russia was waging a war against the West in Ukraine given its supply of weapons to Ukrainian forces.

The EU is set to send further military support to Ukraine under its so-called European Peace Facility, which has already mobilised some €2.5bn.