UK says 'all options are on the table' if Russia uses chemical weapons in Ukraine

All options would be on the table in how the West responds to any use of chemical weapons in Ukraine by Russia, British armed forces minister James Heappey said on Tuesday.

British Foreign Secretary Liz Truss said on Monday Britain was working with its partners to verify the details of reports that Russian forces may have used chemical agents in an attack on the southeastern Ukrainian city of Mariupol, where thousands are believed to have died during a near-seven week siege.

"There are some things that are beyond the pale, and the use of chemical weapons will get a response and all options are on the table for what that response could be," Heappey told Sky News, adding that British defence intelligence so far had been unable to verify the reports.

Asked on LBC Radio whether he could rule out this including deploying British or NATO troops on Ukrainian soil, Heappey said: "No, all options are on the table."

Ukrainian President Volodymyr Zelenskiy said on Monday that Russia could resort to chemical weapons in his country and called on the West to impose stronger sanctions on Moscow that would deter even talk of using such weapons.

"If chemical weapons have been used, that is a very important moment for our prime minister and other heads of government around the world to consider how we would respond to that," Heappey told BBC TV.

"(Russian) President (Vladimir) Putin should be clear that the use of chemical weapons is simply not acceptable and he shouldn't expect the West to stand by if they were used."