President Putin has accused the West of engaging in “nuclear blackmail” and warned he has “lots of weapons to reply”.
In a rare address to the nation, he said he wasn’t bluffing and would use “all the means available to us” if Russian territory was threatened.
Mr Putin also ordered an immediate “partial mobilisation” – calling up military reserves to the Ukraine war – a move that Russia’s defence minister said amounted to around 300,000 troops.
Live: Putin orders ‘partial mobilisation’ in Ukraine and calls up military reservists
“Now they (the West) are talking about nuclear blackmail,” said the Russian leader.
He cited claims of Ukraine shelling the occupied Zaporizhzhia nuclear power plant and said some representatives of NATO states had raised the possibility of using nuclear weapons against Russia.
He warned them his country “has various weapons of destruction, and with regard to certain components they’re even more modern than NATO ones”.
“If there is a threat to the territorial integrity of our country, and for protecting our people, we will certainly use all the means available to us – and I’m not bluffing,” said President Putin.
He also approved referendums in four Ukrainian regions under Russian occupation.
Donetsk, Luhansk, Kherson and Zaporizhzhia announced the plans on Tuesday.
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The are scheduled to take place from 23 to 27 September. Together, the regions make up about 15% of Ukrainian territory.
Ukraine’s foreign minister Dmytro Kuleba has dismissed the plans, saying: “The Russians can do whatever they want. It will not change anything.”
The UK Ministry of Defence said the referendums were probably “driven by fears of imminent Ukrainian attack and an expectation of greater security after formally becoming part of Russia”.
Reserve call-up an ‘admission of failure’
Mr Putin’s speech comes after Ukrainian counterattacks recaptured large swathes of territory in recent weeks.
UK Defence Secretary Ben Wallace said the president’s call-up of reserves had broken one of his own promises and was an “admission that his invasion is failing”.
He tweeted that the president had “sent tens of thousands” of Russians to their death and “no amount of threats and propaganda can hide the fact that Ukraine is winning this war”.
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In his Wednesday morning speech, President Putin again called Ukrainian forces “neo-Nazis” and accused them of carrying out “acts of terror”.
He said 5,937 Russian troops had been killed in the war.
This is much lower than the 40,000+ quoted by Ukraine and the 15,000 estimate given by the head of MI6 in July.
Foreign Office minister Gillian Keegan told Sky News that Mr Putin’s nuclear threat was something to “take very seriously”.
“This is obviously an escalation,” she said.