US President Joe Biden said on Monday that it was "clear" that Russia was considering chemical and biological weapons attacks in Ukraine, warning that such a move would result in a "severe" Western response.
"He has his back to the wall," Biden said of Russian President Vladimir Putin. The US President rebuffed Moscow's allegations that the US has chemical and biological weapons in Europe: "That is simply not true. I guarantee that."
"They (the Russians) also claim that Ukraine has chemical and biological weapons in Ukraine. This is a clear sign that he (Putin) is planning to use these two types of weapons," Biden continued.
These remarks echo warnings issued earlier this month when Russian officials accused Ukraine of hiding a US-backed chemical weapons programme.
"Now that Russia has made its false accusations and China appears to be buying into the propaganda, we need to monitor any possible Russian use of chemical or biological weapons in Ukraine," White House press secretary Jen Psaki said on Twitter.
Biden reiterated on Monday that the use of such weapons would expose Moscow to "severe" retaliation from Western powers "because of NATO's united front." He did not elaborate on what such retaliation would include.
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Biden reaffirmed previous promises of a strong American response in the event of cyber-attacks against vital infrastructure in the United States.
"We had a long conversation about the consequences if he engaged in cyber-attacks," Biden said, referring to a summit with Putin last year in Geneva.
Biden is set to arrive in Brussels to attend a NATO summit and European Council meeting on 24 March, where the Russian invasion of Ukraine will be discussed.