The British Foreign Office says Russia is using a 'troll factory' to spread disinformation about the war in Ukraine on social media and target politicians across a number of countries including Britain and South Africa.
Britain cited UK-funded expert research, which it did not publish.
It said the research exposed how the Kremlin's disinformation campaign was designed to manipulate international public opinion of Russia's invasion of Ukraine, boost support for it and recruit new sympathisers.
Russia calls its actions in Ukraine a "special operation" to disarm Ukraine and protect it from fascists.
Ukraine and the West say the war is an unprovoked act of aggression.
Russia says the Western media have provided an excessively partial narrative of the war that largely ignores Moscow's concerns about the enlargement of NATO and what it says is the persecution of Russian speakers in Ukraine, something denied by Kyiv.
"We cannot allow the Kremlin and its shady troll farms to invade our online spaces with their lies about Putin's illegal war," Britain's Foreign Secretary Liz Truss said in a statement.
"The UK government has alerted international partners and will continue to work closely with allies and media platforms to undermine Russian information operations."
Moscow has denied past accusations by Western countries of disinformation campaigns, for example Washington's accusation Russia sought to meddle in the 2016 US presidential election.
Britain said the research showed the troll factory was using Telegram to recruit and co-ordinate new supporters who then target the social media profiles of Kremlin critics, spamming them with comments in favour of President Vladimir Putin and his war.
Among their targets have been senior British ministers and other world leaders, Britain said, adding traces of the operation had been detected across eight social media platforms including Telegram, Twitter, Facebook and TikTok.