“It’s the latest example of irresponsible behaviour that we have seen from Russia since its full-scale invasion of Ukraine over a year ago,” Miller said, repeating Washington’s warning that use of chemical, biological or nuclear weapons in the conflict would be met with “severe consequences”, without specifying those consequences.

“I will just add we have seen no reason to adjust our strategic nuclear posture or any indications that Russia is preparing to use a nuclear weapon,” Miller said.

(Reporting by Simon Lewis; Editing by Diane Craft, Alexandra Hudson.)