Russia's Ambassador to Britain Andrei Kelin is not expecting his country to deploy tactical nuclear weapons in the war in Ukraine, which experts believe could drag on for a long time.

According to Russian military rules, this would only happen when Russia's existence is threatened, Kelin said in a BBC interview broadcast on Sunday.

"It has nothing to do with the current operation," Kelin said. Moscow refers to its invasion of Ukraine as a "special military operation."

Asked whether President Vladimir Putin would consider attacking Britain with nuclear weapons in case of an expansion of the war, the ambassador rejected this.

This and other scenarios had been publicly discussed on Russian state television several weeks ago.

When shown evidence of Russian war crimes committed in Ukraine, Kelin repeatedly denied Moscow's responsibility for them. "Nothing is happening, no bodies are on the street," he said when asked about the atrocities committed in the Kyiv suburb of Bucha, where hundreds of bodies were found after Russian troops withdrew in early April.

"In our view it is a fabrication. It is used just to interrupt negotiations," Kelin said.

During the interview, the Russian ambassador also repeatedly accused Ukraine of killing civilians in the eastern Donbass region.

Earlier on Sunday, British intelligence charged that Russia was fabricating narratives about the war in Ukraine to muddle the public's understanding of the conflict.

Moscow has "demonstrated it is prepared to leverage global food security for its own political aim and then present itself as the reasonable actor and blame the West for any failure," Britain's Ministry of Defense said in its daily Ukraine intelligence update on Sunday.

The ministry cited an incident when Russia had called on Ukraine a few days ago to de-mine the port of Odessa, in the Black Sea, in order for ships carrying food to safely pass through. However, Russia itself has been blocking the export of grain from Ukrainian ports.

According to London, the incident was "a core tenet of modern Russian messaging strategy: introducing alternative narratives, however unconvincing, to complicate audiences' understanding."

Since the beginning of Russia's invasion of Ukraine on Feb. 24, the British Ministry of Defense has regularly been publishing an intelligence update on the situation.

Moscow has accused London of conducting a targeted disinformation campaign.