Per the Times, Mariupol officials have claimed "that some chemical had been dropped by a drone on the city's sprawling Azovstal steel plant," while Ukrainian military commanders in the area said "that the unknown substance "caused respiratory difficulties and neurological symptoms that can be associated with chemical agents in a handful of soldiers and civilians."
Russian troops have secured the majority of Mariupol, but Ukrainian troops, many of them from the far-right Azov Battalion, still hold the large steel plant on the city's coast. In a statement issued on Telegram, a spokesperson for Azov said they were not able "to investigate the scene of the crime due to enemy fire."
Last month, President Biden warned that if Russian forces used chemical weapons in Ukraine, it "would trigger a response in kind" from NATO. National Security Advisor Jake Sullivan quickly clarified that Biden's remark did not mean the U.S. would respond with its own chemical weapons. A few days, later Biden said Russia's use of chemical weapons would trigger "a significant response" but refused to elaborate on what that might be.