Russia's Defence Ministry said on Saturday that Ukrainian aircraft had struck two industrial sites in the Russian-held city of Luhansk in eastern Ukraine with Storm Shadow long-range cruise missiles supplied by Britain.
Reuters could not verify the battlefield reports.
Britain on Thursday became the first country to say it had started supplying Kyiv with long-range cruise missiles, which will allow it to hit Russian troops and supply dumps far behind the front lines as it prepares a major counteroffensive.
British Defence Minister Ben Wallace said the missiles could be used within Ukrainian territory, implying that he had received assurances from Kyiv that they would not be used to attack targets inside Russia's internationally accepted borders.
The Russian ministry said the missiles had hit a plant producing polymers and a meat-processing factory in Luhansk on Friday.
"Storm Shadow air-to-air missiles supplied to the Kyiv regime by Britain were used for the strike, contrary to London's statements that these weapons would not be used against civilian targets," the ministry said.
It also said Russia had downed two Ukrainian warplanes - an Su-24 and a MiG-29 - that had launched the missiles.
In its latest bulletin, the ministry also said Russian forces had gained control over another block in the eastern city of Bakhmut, which Moscow has been trying to capture for more than 10 months in an attritional artillery battle.
"The units of the Airborne Forces provided support to the assault units and pinned down the enemy on the flanks," it said.
The ministry often uses the term "assault units" to denote the Wagner private militia, which has been spearheading the assault on Bakhmut at great cost in casualties.