Western governments are looking into an alleged chemical weapon attack in Ukraine's southern port city of Mariupol.
UK and US intelligence are investigating unverified reports of chemical weapons being used by Russian forces, saying that they are aware that Russia may have already used chemical agents in Mariupol.
Ukraine's Deputy Defence Minister Hanna Malyar said on Tuesday that his country was checking unverified information that Russia may have used chemical weapons while besieging Mariupol.
"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.