Russia-Ukraine War: Russia's invasion of Ukraine has entered day 48.
Ukraine is checking unverified information that Russia may have used chemical weapons while besieging the southern Ukrainian port city of Mariupol, Ukraine's Deputy Defence Minister Hanna Malyar said on Tuesday.
"There is a theory that these could be phosphorous munitions," Malyar said in televised comments, adding: "Official information will come later."
Russia's defence ministry did not immediately respond to a request for comment.
Ukrainian President Volodymyr Zelenskiy warned on Monday that Russia could use chemical weapons in Ukraine.
Britain and the United States have said they are aware of reports that Russia may have already used chemical agents in Mariupol. Britain said it was working with partners to verify the reports.
Russia has previously accused Ukraine of preparing to use chemical weapons, without providing evidence.
Last month the Kremlin said U.S. talk of Russia using such weapons was a tactic to divert attention away from awkward questions for Washington.
Russia's invasion of Ukraine has killed thousands and displaced millions. Moscow calls its actions in Ukraine a "special operation" to destroy Ukraine's military capabilities and capture what it views as dangerous nationalists, but Ukraine and the West say Russia launched an unprovoked war of aggression.