WASHINGTON

The US warned Russia on Monday that it would face "severe consequences" if it were to use a "dirty bomb" or any other nuclear weapon against Ukraine.

State Department spokesman Ned Price said that should Russia use an improvised nuclear device against Ukraine, it "would certainly be another example of President [Vladimir] Putin's brutality."

"If he were to use a so-called 'dirty bomb,' there would be consequences for Russia, whether it uses a dirty bomb or a nuclear bomb," Price told reporters. He did not outline what types of responses the US is considering.

A dirty bomb combines conventional explosive with radioactive materials that spread across an area following detonation.

Russia has accused Ukraine of preparing to use such a device, a claim the West has rejected as potential cover for the Kremlin to use a dirty bomb.

The US, France and UK flatly rejected the suggestion on Sunday, saying in a joint statement that each of their defense ministers "made clear" in separate phone calls with Russian Defense Minister Sergey Shoygu "that we all reject Russia’s transparently false allegations that Ukraine is preparing to use a dirty bomb on its own territory."

"The world would see through any attempt to use this allegation as a pretext for escalation. We further reject any pretext for escalation by Russia," the countries said.