Boris Johnson has said he fears Russia may use chemical weapons as their forces continue to invade Ukraine.
The Prime Minister said he feared the "barbaric" regime in the Kremlin may be ready to use the banned weapons as the invading Russian forces have failed to make the progress expected.
His warning came as the UK stepped up its sanctions on oligarchs deemed to be close to the Putin regime, including Chelsea owner Roman Abramovich.
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The UK has already accused the Russian government of war crimes, with the bombing of a maternity hospital in Mariupol being the latest atrocity in the campaign.
Western allies fear Vladimir Putin could go further and carry out a chemical attack, potentially under the cover of a "false flag" operation.
Mr Johnson told Sky News’ Beth Rigby: "The stuff which your are hearing about chemical weapons is straight out of the Russian playbook.
"They start saying that there are chemical weapons that are being stored by their opponents or by the Americans, so that when they themselves deploy chemical weapons - as I fear they may - they have a sort of a maskirovka, a fake story, ready to go."
In a reference to the Salisbury nerve agent attack, he added: "You have seen it in Syria, you saw it even in the UK. I just note that is what they are already doing. It is a cynical, barbaric government I'm afraid."
Earlier, Foreign Secretary Liz Truss said the Government was "very concerned" about the potential use of chemical weapons.
She told CNN: "We've seen Russia use these weapons before in fields of conflict, but that would be a grave mistake on the part of Russia, adding to the grave mistakes that have already been made by Putin."
In Mariupol conditions are grim, with food and water running short and some of trapped citizens resorting to melting snow to drink.
Western officials have described the refugee situation in Ukraine as "unprecedented", with concerns that the number of people fleeing could reach four million within days. So far around 2.2 million people have left Ukraine.
One official said: "I would like to stress the sheer scale of this, which is something that we haven't seen, certainly since the end of the Second World War, and that is a real challenge to us all."
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