Downing Street said Vladimir Putin should “end the onslaught and needless bloodshed” after he lowered the threshold at which Russian forces could use nuclear weapons.
Asked what Britain’s response to the move was, a Number 10 spokesperson said: “Our focus remains on supporting Ukraine … we’re very clear that Vladimir Putin could end this war tomorrow.
“He could remove his troops, roll back his tanks and end the onslaught and needless bloodshed in both Ukraine and Russia. That is entirely within his gift.
“We would urge him to do so.”
They added: “We will continue to support (the Ukrainian people) for as long as is necessary in their fight against an illegal invasion.”
President Vladimir Putin signed the revised nuclear doctrine on Tuesday morning, declaring that an attack on Russia by any nation supported by a nuclear power will be considered a joint attack on his country.
His endorsement of the new nuclear deterrent policy follows President Joe Biden’s decision to let Ukraine strike targets inside Russia with US-supplied long-range missiles.
There is now speculation that the UK could follow the US and allow Ukraine to use British Storm Shadow missiles in Russia.
The Kremlin criticised Biden’s decision on Monday evening, saying he was adding “fuel to the fire” and warned the decision would escalate international tensions.
Tensions have increased in recent months after thousands of North Korean troops were deployed as part of Russia’s offensive, sparking concern that their entry could lead to a new phase in the war.
Addressing the European parliament on Tuesday, Volodymyr Zelenskyy said 11,000 North Korean troops had been deployed, but this could increase to 100,00.
When asked whether the updated doctrine was deliberately issued because of Biden’s decision, Kremlin spokesperson Dmitry Peskov said the document was published “in a timely manner” and that Putin instructed the government to update it earlier this year so that it is “in line with the current situation.”
Putin first announced changes in the nuclear doctrine in September, when he chaired a meeting discussing the proposed revisions.
He has previously warned the US and other NATO allies that allowing Ukraine to use Western-supplied longer-range weapons to hit Russian territory would mean that Russia and NATO are at war.
The updated doctrine states that an attack against Russia by a nonnuclear power with the “participation or support of a nuclear power” will be seen as their “joint attack on the Russian Federation.”
It adds that Russia could use nuclear weapons in response to a nuclear strike or a conventional attack posing a “critical threat to sovereignty and territorial integrity” of Russia and its ally Belarus.
On Monday, the Prime Minister refused to confirm if the UK will allow Ukraine to use the long-range missiles in Russia, but said that Ukraine is “number one” on his agenda whilst at the G20 in Brazil.
He said that he is “not going to get into operational details” with regards to missiles in Ukraine “because the only winner, if we were to do that, is (Vladimir) Putin.”
Ministers on Monday also hinted at a possible change, saying Britain was working in close co-operation with America and would align with allies in ensuring Kyiv could make use of the capabilities that had been offered.
Speaking at a UN Security Council session on Monday, Foreign Secretary David Lammy said the UK will “never let up” in backing Ukraine.
He warned that unless Putin fails, faith in international law may “never return”.
Addressing delegates in New York, Lammy said: “Unless Putin fails, we could plunge into a world where the principles inscribed in the UN charter will have lost their meaning.
“Unless Putin fails, others will be inspired to wage imperialist wars of conquest. Unless Putin fails, our faith in international law may never return. Unless Putin fails, each of our borders will be less safe.”
Lammy’s message comes as Kyiv and Western allies brace for a possible change of US stance under Donald Trump, who has said he could end the war “in a day”.
Asked how concerned he was about the change of US leader as he spoke with the press outside the UN Security Council meeting, the Foreign Secretary said: “I’ve studied in this country, I’ve worked in this country, and I know that there’s a simple rule: one president at a time.
“We’re dealing with President Biden and we are committed to putting Ukraine in the strongest possible position.”
He added: “We will help keep the lights of Ukraine on in the face of Putin’s aggression, and that matters not just for Ukraine’s security, Britain’s security or indeed Europe’s security.”
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