Alexander Ermochenko | Reuters WASHINGTON – Defense Department spokesman John Kirby said the Pentagon was closely monitoring reports Monday night of a possible Russian chemical weapons attack in the besieged Ukrainian city of Mariupol. If Russia were found to have used chemical weapons in the strategic stay of the city, it would represent a large-scale escalation of the conflict and an immediate challenge for NATO to act. “We have reports on social media claiming that Russian forces have developed possible chemical munitions in Mariupol, Ukraine,” Kirby said on Monday. “We can not confirm at this time and will continue to monitor the situation closely.” “These reports, if true, are deeply troubling and reflect the concerns we have had about Russia’s ability to use a variety of riot control agents, including tear gas canisters, in Ukraine,” he said. British Foreign Secretary Liz Tras also said her government was working “urgently” to verify details of the alleged attack. The original report was in the form of a Telegram message published by the Azov Constitution, a supranationalist section of the Ukrainian National Guard. Azov’s message said Russian forces had used “a poisonous substance of unknown origin”. “Any use of such weapons would be a harsh escalation in this conflict and we will hold Putin and his regime accountable.” wrote Troy on Twitter. U.S. officials have warned for several days that the Russian military will almost certainly continue to commit what it calls “atrocities” as it doubles its attacks in eastern Ukraine. “Russian leaders have shown in the past … the barbarity with which they conduct and prosecute their operations,” Kirby told reporters earlier Monday, citing the alleged use of chemical weapons by Russia during the Syrian civil war as an example. of war. This is breaking news. Check again for updates.