President Vladimir Putin has ordered Russian nuclear deterrent forces on alert amid tensions with the West over his invasion of Ukraine.
Speaking at a meeting with his top officials, Mr Putin asserted that leading Nato powers had made "aggressive statements" along with the West imposing hard-hitting financial sanctions against Russia, including the president himself.
Mr Putin ordered the Russian defence minister and the chief of the military's General Staff to put the nuclear deterrent forces in a "special regime of combat duty".
Read more: Get all our live updates from Russia's invasion of Ukraine here
It comes as Foreign Secretary Liz Truss said any use of nuclear or chemical weapons would represent an "extremely serious escalation" of the conflict which could see Russian leaders brought before the International Criminal Court.
Her warning followed comments from the Commons Defence Committee chairman Tobias Ellwood who said that in the "worst-case scenario" Mr Putin could deploy low yield tactical nuclear weapons if his forces failed to make a breakthrough.
With the Russian advance on the capital, Kyiv, apparently bogged down in the face of fierce Ukrainian resistance, Ms Truss said the survival of Mr Putin's regime could now be at stake if his invasion plan failed.
"This could well be the beginning of the end for Putin. I fear that he is prepared to use the most unsavoury means in this war," she told Sky News' Trevor Phillips on Sunday programme.
When asked about Russia's arsenal of chemical and tactical nuclear weapons, she said: "I fear this conflict could be very, very bloody.
"I urge the Russians not to escalate this conflict but we do need to be prepared for Russia to seek to use even worse weapons. I think it would be hugely devastating. We need to avoid this at all costs."
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