The UK warned on Saturday that Russia was plotting to install a pro-Moscow leader in Ukraine at a time of mounting western alarm over an imminent Russian invasion of the country.

The Foreign, Commonwealth and Development Office said it had evidence that Russia’s president Vladimir Putin was seeking to install a puppet regime as it mulls whether to invade — and named Yevhen Murayev, a former Ukrainian MP, as a potential leader favoured by Moscow. It did not release that evidence.

Liz Truss, UK foreign secretary, said that the revelation “shines a light on the extent of Russian activity designed to subvert Ukraine and is an insight into Kremlin thinking”.

She added: “Russia must de-escalate, end its campaigns of aggression and disinformation, and pursue a path of diplomacy. As the UK and our partners have said repeatedly, any Russian military incursion into Ukraine would be a massive strategic mistake with severe costs.”

Murayev is a pro-Russian politician from the northern Ukrainian city of Kharkiv. He is a former member of the Party of the Regions, the party of Viktor Yanukovich, the pro-Russian president who was ousted in the Maidan revolution in 2014. Murayev created his own party Nashi, named after the Russian youth movement, but is a fairly minor political figure.

Russia itself placed sanctions on Murayev, who owns a major TV station, in 2018. On Saturday he posted on his Facebook profile a picture of his face photoshopped on to an image of James Bond and wrote “Details tomorrow”, adding a smiley emoji.

“I have been under Russian sanctions since 2018 because of my conflict with [Viktor] Medvedchuk,” Murayev told pro-Russian website Strana, referring to a rival pro-Moscow politician close to Putin whose allies the US accused of being pawns in a similar Russian plot earlier this week.

“My family’s assets there have been seized. How the UK secret services and the Foreign Office square that with Russia supposedly wanting to make me the head of an occupation government — that’s a question for Mr Bean,” he added.

Ukraine’s parliament has about 50 members who are supportive of Moscow and opposed to Ukraine’s western alignment.

The UK also highlighted four other former Ukrainian politicians who it said had continued links with Russian intelligence services: Serhiy Arbuzov, former first deputy prime minister of Ukraine; Andriy Kluyev, former chief of staff to Yanukovich; Vladimir Sivkovich, ex-deputy header of Ukraine’s National Security and Defence Council; and Mykola Azarov, former prime minister of Ukraine. All four are believed to be in exile in Russia.

The US treasury department placed sanctions on Sivkovich this week, saying that in 2021 he had “worked with a network of Russian intelligence actors to carry out influence operations that attempted to build support for Ukraine to officially cede Crimea to Russia in exchange for a drawdown of Russian-backed forces in the Donbas”, where separatists continue to receive support from Russia.

The treasury department also accused Sivkovich of working with Russian intelligence services in 2020 to promote disinformation about the US presidential election.

Russia has massed 106,000 troops on the border with its western neighbour and Nato officials fear a Russian invasion is impending.

Britain’s claims of a Russian plot — released in a statement late on Saturday — are a highly unusual disclosure of intelligence, but fit a pattern of western diplomacy in recent months designed to call out Russian plans for military action or destabilisation of Ukraine.

In response to London’s warning, the Russian foreign ministry said in a statement cited by state newswire RIA Novosti: “The disinformation spread by the UK Foreign Office is yet more evidence that it is Nato countries, foremost the Anglo-Saxons, who are escalating tensions around Ukraine.”

“We call on the Foreign Office to end its provocative activity, stop spreading nonsense and concentrate on studying the history of the Tatar-Mongol yoke,” the ministry added in an apparent dig at UK defence secretary Ben Wallace’s recent speech on Russia and Ukraine’s shared history.

Washington expressed its concern at the allegations. Emily Horne, a spokesperson for the White House’s National Security Council, said: “This kind of plotting is deeply concerning. The Ukrainian people have the sovereign right to determine their own future, and we stand with our democratically elected partners in Ukraine.”

The White House said Biden met with his national security team on Saturday, and “affirmed that if Russia further invades Ukraine, the United States will impose swift and severe consequences on Russia with our Allies and partners”.

The UK’s statement came at the end of a day when Germany’s naval chief resigned after sparking a diplomatic row by saying that Vladimir Putin should be given the “respect he probably deserves” and claiming that Crimea would never be returned to Ukraine.