President Joe Biden has warned that Vladimir Putin is considering using weapons of mass destruction in Ukraine because his “back is against the wall” following the spectacular failure of the first phase of his invasion.

Warnings from Moscow that Ukraine possesses biological and chemical weapons are a ‘clear sign’ that Putin is considering using ‘both of those,’ according to Biden, following a well-established pattern of Russian disinformation in which accusations are used to provide cover for the Kremlin’s own actions.

Russia recently accused the US of storing WMDs in Europe, which Biden dismissed as “simply not true, I guarantee you,” as well as funding bioweapons labs in Ukraine. The United States acknowledges funding Ukrainian labs, but claims they are used to detect disease outbreaks and for bio-defense.

Any use of either weapon in Ukraine would elicit a’severe’ response from the US and NATO, Biden said last night, repeating his earlier remarks but refusing to specify what the allies would do.

He spoke as Ukrainian President Volodymyr Zelensky declared that he would not bow to Russian “ultimatums” and that Ukraine “would have to be destroyed” before he would be willing to simply hand over pieces of the country to Moscow.

It came after Mariupol, which had been under siege for more than three weeks with no access to water, electricity, or food, rejected a Russian offer of surrender in exchange for humanitarian aid. Officials said Russian promises of amnesty could not be trusted, and troops were prepared to fight “to the death.”