Ukraine is reacting “seriously” to UK Foreign Office allegations that Moscow has plans to invade the country and install a puppet government, a senior government adviser has said, adding that Kyiv is resisting Russian efforts to destabilise its government and economy. The extraordinary Foreign Office claims that Moscow may topple the government and install Yevhen Murayev, a former MP who controls a pro-Russia television station, were met with shock and some scepticism in Ukrainian political and media circles on Sunday. The Foreign Office made the allegations as the UK pledged to take a more aggressive posture over Russia’s buildup of more than 100,000 troops and weaponry on the border with Ukraine. Murayev himself denied that he was involved in any plot, telling the Observer he had been banned from entering Russia and was in a conflict with a close ally of Vladimir Putin. “It isn’t very logical,” he said. On Sunday he said he was prepared to defend his “honest name” against the British allegations and he posted a picture on Facebook of himself altered to look like James Bond. But an adviser to the Ukrainian president Volodymyr Zelenskiy’s chief of staff said the alleged plot matched Russian efforts to promote discord in Ukraine. Mykhailo Podolyak told Reuters that although there was doubt among Ukrainians as to whether Murayev was “too ridiculous a figure” to be the Kremlin’s pick to lead Ukraine, Russia had propped up previously minor figures in leadership positions in annexed Crimea and separatist-held Donbass, and that therefore “one should take this information as seriously as possible”. In separate comments to Agence-France Presse, Podolyak said: “Our state will continue its policy of dismantling any oligarchic or political structures that could be working to destabilise Ukraine” or aid Russia. The Kremlin had for some time followed a formula of selecting individuals in business or politics and then using those people to “promote Russia’s interests”, Podolyak said, and “this British information clearly follows along in this logical chain”. The Foreign Office has not provided any evidence to support the allegations, which came as Boris Johnson’s domestic political troubles deepened. British sources emphasised on Sunday afternoon that the coup plot warning on Saturday followed a UK intelligence assessment, a different formulation from earlier briefings that had suggested it was based on “US-led intelligence”. The UK allegation came days after the US alleged that Russian intelligence was recruiting current and former Ukrainian government officials to take over the government in Kyiv and cooperate with a Russian occupying force The accusations have increased tensions as discussions rage about how best to deter Vladimir Putin from launching a new invasion of Ukraine. Russian tanks and artillery, military vehicles and fighter aircraft continued to arrive within striking distance of Ukraine’s borders this weekend, and Russian troops have been sighted less than 20 miles from the border. Moscow has announced sweeping naval exercises that will put its ships in close proximity with Nato forces while potentially positioning landing craft for an amphibious assault on Ukraine’s southern coast. Before a foreign ministers meeting in Brussels on Monday, a senior European official said the EU would be ready to launch sanctions “within days” if Russian troops launch an invasion. The meeting is partially meant to address divisions in the EU over how to deter Russia, with Germany hesitant to provide lethal arms to Ukraine or target the Russian banking sector. Other states have called for pre-emptive sanctions against Russia in order to show the Kremlin that western countries are resolved to strike back in case of an invasion of Ukraine. But the US secretary of state, Antony Blinken, rejected that idea during a television appearance on Sunday, saying it would not work to deter a potential Russian attack. “When it comes to sanctions, the purpose of those sanctions is to deter Russian aggression. And so if they are triggered now, you lose the deterrent effect,” Blinken told CNN’s State of the Union in an interview. Blinken also said he had “no doubts” Germany was maintaining a united front with Nato on the crisis, after its navy chief, Kay-Achim Schönbach, said Putin deserved respect and suggested it was “nonsense” to think Russia was ready to pour troops into Ukraine. Schönbach resigned on Saturday, but his remarks rattled Nato. The Kremlin has denied it is sabre-rattling as it announces snap drills and continues to deploy troops toward Ukraine, waving off the UK’s accusations of a plot to topple the government as “disinformation”. “The disinformation disseminated by the UK foreign ministry is more evidence that it is namely Nato countries led by the Anglo-Saxons who are engaged in the escalation of tensions around Ukraine,” the Russian foreign ministry said on Sunday. Nonetheless, the growing scope of the Russian military exercises amid an urgent European security crisis has worried western observers. The Irish government has decried plans for Russian warships and bombers to conduct missile tests 150 miles off the south-west coast of County Cork next month. And Russia’s northern fleet is preparing to hold military drills this week in an area that overlaps with Norway’s exclusive economic zone, the Barents Observer news website reported. A spokesperson for the Norwegian joint headquarters told the outlet that Norway would monitor the drills but that Russia had the right to hold exercises in international waters.