The PM was asked by journalists if the UK should be preparing for nuclear war at a press conference to close the G20 summit of the world’s largest economies in Brazil.
He replied: “There is irresponsible rhetoric coming from Russia and that’s not going to deter our support for Ukraine.”
Speaking of how there had already been “1,000 days of sacrifice”, Sir Keir said the UK would continue to ensure Ukraine has what it needs to fight the war “for as long as it needs”.
“On day 1,000 of the war I say again – end the war, get out of Ukraine and in this moment when global challenges are affecting us at home, I take the view that British leadership matters,” he added.
Sir Keir noted that Putin had been absent from the G20 for the third year running, adding he was “the author of his own exile”.
The UK has also supplied Ukraine with its Storm Shadow missiles and defence officials but ministers have refused to be drawn on the details about their use by Ukraine following the decision by the White House.