The Biden administration publicly warned Wednesday that Russia might seek to use chemical or biological weapons in Ukraine as the White House rejected Russian claims of illegal chemical weapons development in the country it has invaded.

       Russian Foreign Ministry spokeswoman Maria Zakharova this week, without evidence, accused Ukraine of running chemical and biological weapons labs in its territory, supported by the U.S. White House press secretary Jen Psaki called Russia’s claim “preposterous” and said it could be part of an attempt by Russia to lay the groundwork for itself using such weapons of mass destruction against Ukraine.

       “This is all an obvious ploy by Russia to try to justify its further premeditated, unprovoked, and unjustified attack on Ukraine,” Psaki tweeted Wednesday. “Now that Russia has made these false claims, and China has seemingly endorsed this propaganda, we should all be on the lookout for Russia to possibly use chemical or biological weapons in Ukraine, or to create a false flag operation using them.”

       The U.S. for months has warned about Russian “false flag” operations to create a pretext for the invasion. Wednesday's warning suggested Russia might seek to create a pretense for escalating the two-week old conflict that has seen the Russian offensive slowed by stronger-than-expected Ukrainian defenders, but not stopped.

       Pentagon press secretary John Kirby on Wednesday called the Russian claim “a bunch of malarkey.”

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       The international community for years has assessed that Russia has used chemical weapons before in carrying out assassination attempts against Putin enemies like Alexey Navalny and former spy Sergei Skripal. Russia also supports the Assad government in Syria, which has used chemical weapons against its people in a decade-long civil war.

       Asked by a Russian journalist about the claims, United Nations spokesman Stephane Dujarric said. "At this point have no information to confirm these reports or these allegations about these kinds of labs.”

       “Our colleagues at the World Health Organization, who have been working with the Ukrainian Governments, said they are unaware of any activity on the part of the Ukrainian Government which is inconsistent with its international treaty obligations, including on chemical weapons or biological weapons," Dujarric added.