Defence Secretary Ben Wallace has said an imposter called him up pretending to be the Ukrainian Prime Minister and asked several "misleading questions".
The top Tory blasted the move as a "desperate attempt" by Russia to divert attention away from its brutal invasion of Ukraine in what appeared to be a security breach.
It was not clear how an imposter was able to reach the Defence Secretary, who travelled to Poland on Thursday for talks on the Ukraine conflict.
Mr Wallace has ordered an immediate inquiry to find out how the impostor was able to speak to him.
He tweeted: "Today an attempt was made by an imposter claiming to be Ukrainian PM to speak with me.
"He posed several misleading questions and after becoming suspicious I terminated the call.
"No amount of Russian disinformation, distortion and dirty tricks can distract from Russia's human rights abuses and illegal invasion of Ukraine. A desperate attempt."
The video call was set up after an email, purportedly sent from an aide at the Ukrainian embassy, was sent to a government department and then forwarded to the Ministry of Defence.
Mr Wallace was put through on Teams to the "PM of Ukraine", who was posing with the country's flag behind him.
After initial introductions and thanks for the UK's support, Mr Wallace is understood to have became suspicious as the man started asking questions about British policy and eventually urged the Defence Secretary to shout slogans.
The level of sophistication involved in the hoax has convinced Government sources that it was a Russian plot.
Senior Ministry of Defence sources fear Moscow may attempt to splice together Mr Wallace's comments in an attempt to embarrass him.
Russian pranksters duped the-then Foreign Secretary Boris Johnson into discussing the UK's relationship with Moscow back in 2018 by pretending to be the Armenian Prime Minister.
It comes as Mr Wallace travelled to Warsaw on Thursday, where he announced that the UK would deploy a medium-range missile system and 100 personnel to Poland to "protect her airspace from any further aggression by Russia".
Meanwhile, Russian forces are trying to “pulverise” Ukrainian cities after getting “bogged down” and meeting “fierce” resistance, Western officials warned.
Kremlin troops were “making little bits of progress here and there, but they are not achieving a strategic breakthrough at any point”, they said.
Vladimir Putin 's invaders have “taken substantial casualties” and a death toll of 7,000 was “not an implausible estimate”.
Military top brass have ordered reservists from “some quite peripheral places around Russia and its borders, which clearly was not part of the original plan”, they added.
The redeployments “demonstrate the extent to which Russia has got bogged down”, with morale among its soldiers “very, very low”.
Kremlin warplanes have still failed to win the aerial battle with Ukraine’s air force, with the skies “heavily contested” and Moscow fighter planes moving with “considerable caution” to dodge air defences.
An official said: “It’s clearly not going the way Russia planned it.”
Warning of an intensification of artillery strikes on major population centres, they went on: “The Russian strategy appears to be to bombard city centres to try and pulverise the resistance within them and to encircle them wherever possible.
“I would expect that to continue.”
Kremlin military planners may be unsure of whether to launch a full attack on the capital, Kyiv, it is understood.
“I think there is a question now as to whether Moscow intends to assault Kyiv or not,” one official said.
“To do so, with or without bombardment, would be very costly for Russia.”
They added: “An ill-judged ground assault on a city as well prepared as Kyiv, with really determined and committed defenders would be a very costly business.
“There comes a point where even Russia has to count the cost of casualties.”
