US President Joe Biden has warned that he believes Vladimir Putin is "ready to use" chemical weapons in his quest to complete the invasion of Ukraine.
The brash statement from the White House comes as Russia's invasion of Ukraine enters a 27th day.
There were further attacks overnight on Monday, with a strong statement from the Ukrainian President in response.
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Speaking at a business event on Monday, Mr Biden said that the US intelligence believed that Putin's "back is against the wall and now he’s talking about new false flags he’s setting up including, asserting that we in America have biological as well as chemical weapons in Europe – simply not true. I guarantee you.
"They are also suggesting that Ukraine has biological and chemical weapons in Ukraine. That’s a clear sign he’s considering using both of those. He’s already used chemical weapons in the past, and we should be careful of what’s about to come." he added.
Mr Biden noted that there would be "severe consequences" from NATO if Putin did opt to use chemical weapons.
President Zelenskyy said that his country "will never bow to ultimatums" from Russia, after an incident on Monday.
The Russian forces had said they would open humanitarian corridors in the city of Mariupol - if the Ukrainian army surrendered in the city.
Over 300,000 people are trapped in the encircled region, which has seen bombs rain down upon maternity hospitals, children's hospitals, theatres and schools in recent weeks.
But Mr Zelenskyy has said that no Ukrainian city would accept Russian occupation.
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