After reports emerged Monday of a possible strike involving chemical substances of some kind in Mariupol, the Ukrainian President warned the possibility should be taken seriously, though a Mariupol official said any such attack remained unconfirmed.
In his nightly address Monday, President Volodymyr Zelensky said Russia might be preparing to escalate attacks on the besieged southeastern city.
"Today, the occupiers issued a new statement, which indicates that they are preparing a new stage of terror against Ukraine and our defenders. One of the occupiers' spokesmen said that they could use chemical weapons against the defenders of Mariupol. We take this as seriously as possible," Zelensky said.
Petro Andryushchenko, adviser to the mayor of Mariupol, posted on Telegram shortly before Zelensky’s address that information about a possible chemical attack "is not yet confirmed," adding, "details and clarifications later."
"In any case, the announcement of the use of chemical weapons made by the occupier is not so simple," Andryushchenko said. "It is possible that the discharge of an unknown chemical is a test for the reaction in general. One scenario. But we are waiting for official information from the military."
UK investigates: Also on Monday, UK Foreign Secretary Liz Truss tweeted that she was working “urgently with partners” to investigate the reports of a possible chemical attack in Mariupol.
“Reports that Russian forces may have used chemical agents in an attack on the people of Mariupol. We are working urgently with partners to verify details. Any use of such weapons would be a callous escalation in this conflict and we will hold Putin and his regime to account," Truss wrote.
CNN cannot independently verify that there has been any kind of chemical strike in Mariupol.
CNN teams on the ground have so far not seen evidence of such an attack, or any imagery from Mariupol sources to verify this.