UK warns Russia of severe consequences if nuclear weapons used in Ukraine

British Foreign Secretary James Cleverly speaks during an interview with Reuters in New Delhi

LONDON (Reuters) - Britain on Monday warned Russian President Vladimir Putin of severe consequences if Moscow uses nuclear weapons in Ukraine, saying such a step would change the nature of the conflict.

Foreign Secretary James Cleverly also urged Russia not to impede grain exports, and said that "increasingly desperate statements" from the Kremlin were designed to distract from its faltering war effort.

Putin has said that Russia hasn't talked about using nuclear weapons in Ukraine, saying instead that Kyiv could create and detonate a "dirty bomb".

But Cleverly said it was an "absurd claim" to say Ukraine planned to detonate such a bomb, adding that Putin's rhetoric around nuclear weapons was "irresponsible talk".

"No other country is talking about nuclear use. No country is threatening Russia or President Putin," Cleverly told lawmakers.

"He should be clear that for the UK and our allies, any use, at all, of nuclear weapons would change the nature of the conflict. There would be severe consequences for Russia."

Russia's defence ministry said that British navy personnel blew up Nord Stream gas pipelines last month, and that "British specialists" from the same unit directed Ukrainian drone attacks on its Russian Black Sea fleet in Crimea on Saturday.

Britain has said the accusations are false. Cleverly did not directly reference those comments, but said: "Now the Kremlin is resorting to peddling false claims, churning out invented stories that say more about the fractures within Russia's government than they do about us."

Russia on Saturday suspended its participation in a U.N.-brokered Black Sea grain deal, citing the drone attack on its fleet.

Cleverly said it would be "unconscionable" for people in low and middle income countries to suffer as a result.

"I urge Russia to stop impeding this vital initiative that is feeding the hungry across the world and agree to its extension," he said.

(Reporting by William James and Alistair Smout. Editing by Andrew MacAskill)