Vladimir Putin has responded to "aggressive statements" by NATO countries. | Russian Pool

Vladimir Putin has placed Russia's nuclear deterrent on "special alert", a move denounced by the US Ambassador to the United Nations, Linda Thomas-Greenfield, as "totally unacceptable". "It means that President Putin is continuing to escalate this war in a manner that is totally unacceptable and we have to continue to stem his actions in the strongest possible way."

The move is being interpreted as a warning to NATO rather than indicating an intent to use nuclear weapons. It follows Putin's own denouncement of "illegitimate" economic sanctions by the USA, the European Union, the UK and Canada in excluding certain Russian banks from the Swift international payment system and paralysing international assets of the Russian Central Bank. He has also referred to "aggressive statements" by NATO countries.

Ukraine's president, Volodymyr Zelensky, has meanwhile released a statement saying that a Ukrainian delegation will meet a Russian delegation "without preconditions" on the Ukrainian-Belarusian border.