UK 'very concerned' Russia may use chemical weapons, says British foreign secretary

British Foreign Secretary Liz Truss said Thursday that the U.K. is "very concerned" that Russian President Vladimir Putin may potentially order the use of chemical weapons in Ukraine.

Appearing on CNN, Truss said it would be a "grave mistake on the part of Russia, adding to the grave mistakes that have already been made by Putin."

"We've seen Russia use these weapons before in fields of conflict," said Truss, who is currently visiting the U.S.

During her trip, Truss is expected to encourage Washington to "ramp up the global pressure" on Russia. According to an advance copy of Truss's speech to the Atlantic Council obtained by Reuters, she will say sanctions "must go further."

On Wednesday, the White House similarly warned that Russia may use chemical weapons in Ukraine or launch a false flag operation as a pretext for using such weapons. This came after Russia accused the U.S. of operating biowarfare laboratories in Ukraine.

"We took note of Russia's false claims about alleged U.S. biological weapons labs and chemical weapons development in Ukraine. We've also seen Chinese officials echo these conspiracy theories," White House press secretary Jen Psaki said.

Psaki pointed to Russia's "well-documented track record of using chemical weapons, including in attempted assassinations and poisoning of Putin's political enemies like Alexey Navalny."

"This is preposterous," she added. "It's the kind of disinformation operation we've seen repeatedly from the Russians over the years in Ukraine and in other countries, which have been debunked, and an example of the types of false pretexts we have been warning the Russians would invent."