Boris Johnson says he fears Russia could use chemical weapons on Ukraine.
The Prime Minister has accused Vladimir Putin of a 'cynical' attempt to manufacture a pretext for their use.
He said he feared the 'barbaric' regime in the Kremlin may be ready to use the banned weapons because 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.
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 Moscow could go further and carry out a chemical attack, potentially under the cover of a 'false flag' operation.
"The stuff which your are hearing about chemical weapons is straight out of the Russian playbook," Mr Johnson told Sky News in an interview today. 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 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."
His comments came as it was confirmed three people - including a young girl - were killed in the bombing of a hospital in Mariupol yesterday, the city's council announced, with 17 said to have been injured.
Speaking on Sky News' Beth Rigby Interviews programme, the prime minister said the only way the war in Ukraine can end is if the Russian president realises he has made a 'catastrophic mistake'.
Home Secretary Priti Patel was urged to do more to make it easier for Ukrainians to find sanctuary in the UK after announcing a limited series of changes to the visa regime.
From Tuesday many Ukrainians will be able to apply online for permission to come under the scheme allowing family members to be reunited with relatives already settled in the UK. But the British Red Cross said the quickest way of fixing the problem would be to remove the requirement for a visa, while the Refugee Council said Ms Patel’s announcement “does not go anywhere near far enough".
Ministers have insisted that visa checks are required to make sure Vladimir Putin does not send Russian agents posing as refugees.
But the scale of the humanitarian crisis has led to demands for the UK to take in more Ukrainians, with up to four million people expected to flee the war zone. So far around 2.2 million people have left in a crisis unseen in Europe since the Second World War.
Meanwhile Ukraine’s foreign minister said talks between the top diplomats of Moscow and Kyiv produced no breakthrough on ending the war following Russia’s invasion.
Ukrainian foreign minister Dmytro Kuleba said he attended the meeting on Thursday with Russian counterpart Sergei Lavrov in Turkey to discuss humanitarian corridors and a ceasefire. Mr Kuleba said there are “other decision-makers” in Russia who need to be consulted, adding that he agreed with Mr Lavrov to continue to seek a solution to humanitarian issues caused by the war.
He said Moscow is not ready to offer a ceasefire, adding: "They seek Ukraine’s surrender. This is not going to happen."
