Last week, the UN said it had no evidence Ukraine had a biological weapons programme.
Britain's Defence Ministry said in a tweet on Monday that Russia could be planning to use chemical or biological weapons in Ukraine in response to a staged fake attack on Russian troops.
It cited no evidence to support the assertion in what it called an intelligence update. U.S. officials have made similar statements.
The Twitter post said:"Such an operation could take the form of a faked attack, a staged 'discovery' of agents or munitions or fabricated evidence of alleged Ukrainian planning to use such weapons."
It said the Defence Ministry had seen no evidence to support Russia's accusations that Ukraine planned to use chemical and biological weapons.
The United Nations on Friday said it had no evidence Ukraine had a biological weapons program while Washington and its allies accused Russia of spreading the unproven claim as a possible prelude to launching its own biological or chemical attacks.
Speaking to reporters on Friday, U.S. President Joe Biden warned Russia that it would pay a "severe price" if its military should use chemical weapons against Ukraine.
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