A UK minister warned Tuesday any use of chemical weapons by Russia in its attacks on Ukraine "will get a response and all options are on the table".
The stark warning came hours after London said it was trying to verify reports Moscow used chemical weapons Monday in the besieged Ukrainian city of Mariupol.
"If they are used at all, then (Russian) President (Vladimir) Putin should know that all possible options are on the table in terms of how the West might respond," armed forces minister James Heappey told Sky News.
"There are some things that are beyond the pale, and the use of chemical weapons will get a response."
Foreign Secretary Liz Truss said hours earlier that Britain was working with partners to verify the reports that Russian forces may have used chemical agents in Mariupol.
"Any use of such weapons would be a callous escalation in this conflict and we will hold Putin and his regime to account," she added on Twitter.
Reports first emerged earlier Monday from Ukraine's Azov battalion that a Russian drone had dropped a "poisonous substance" on troops and civilians in Mariupol.
The force claimed people were experiencing respiratory failure and neurological problems.
"Three people have clear signs of poisoning by warfare chemicals, but without catastrophic consequences," battalion leader Andrei Biletsky said in a video message on Telegram.
He accused the Russians of using the chemical weapons during a strike on the city's large Azovstal metallurgical plant.
AFP has been unable to verify the claims, which were shared by Ukrainian lawmakers.
'Deeply concerning'
A strategic port located along the Sea of Azov, Mariupol has been besieged for weeks and Ukrainian forces are warning of its imminent fall.
An aide to its mayor noted on Telegram the alleged chemical attack "is not currently confirmed".
"We are waiting for official information from the military," Petro Andryushchenko wrote.
US Pentagon Press Secretary John Kirby said late Monday that Washington was aware of the reports but could not confirm them.
"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," he said.
Eduard Basurin, a senior official in the separatist area of Donetsk in eastern Ukraine, has spoken of the possibility of chemical weapons being used in Mariupol.
Basurin said the besieging forces could "turn to chemical troops who will find a way to smoke the moles out of their holes," Russian news agency RIA Novosti quoted him as saying on Monday.
Russia has denied committing any war crimes during what it calls its special military operations in Ukraine.
In its daily intelligence update on the conflict, Britain's Ministry of Defence said the Kremlin was continuing to "refocus its efforts" on the country's east.
"Russian forces continue to withdraw from Belarus in order to redeploy in support of operations in eastern Ukraine," it added.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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