The UK Foreign Secretary says Russia may have used a "chemical agent" in an attack on Ukraine, further escalating the conflict.
Liz Truss revealed the UK Government is investigating the claims on Tuesday.
"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," Truss tweeted.
"Any use of such weapons would be a callous escalation in this conflict and we will hold [Vladimir] Putin and his regime to account."
It comes after Ukraine said tens of thousands of people have likely been killed in Russia's assault on the southeastern city while the country's rights ombudswoman accused Russian forces in the region of torture and executions.
Widespread destruction has been confirmed in Mariupol but allegations of crimes and the estimate of those killed in the city are yet verified.
"Mariupol has been destroyed, there are tens of thousands of dead, but even despite this, the Russians are not stopping their offensive," President Volodymyr Zelensky but he didn't provide any further details.
Earlier on Tuesday, the Ukrainian Parliament said they have received reports from police that Russian forces have fired on nitric acid tanks in the city of Donetsk, which is a two-hour drive south of Mariupol.
Officials are urging locals to prepare face masks soaked in a soda solution to protect them from the acid.
This comes as a spokesperson for Russia’s proxies in Donbas, the region Donetsk is in, appeared to promote the idea of using chemical agents.
"We should ask our chemical forces to find a way to smoke these moles out of their holes," spokesperson Eduard Basurin said according to the Kyiv Independent.
The outlet also reported that Russian forces used a drone to drop a "poisonous substance" on Ukrainian troops, with three people reportedly showing clear signs of chemical poisoning.
The United States Department of Defense headquarters, the Pentagon, said it is alarmed by the reports of chemical ammunition being used and is monitoring the situation closely.
"We are aware of social media reports which claim Russian forces deployed a potential chemical munition in Mariupol, Ukraine. We cannot confirm at this time and will continue to monitor the situation closely," Defense Department spokesman John Kirby told U.S. News.
"These reports, if true, are deeply concerning and reflective of concerns that we have had about Russia’s potential to use a variety of riot control agents, including tear gas mixed with chemical agents, in Ukraine."
