The UK has accused President Putin of plotting to install a pro-Moscow figure to lead Ukraine's government.
The Foreign Office took the unusual step of naming former Ukrainian MP Yevhen Murayev as a potential Kremlin candidate.
Russia has moved 100,000 troops near to its border with Ukraine but denies it is planning an invasion.
UK ministers have warned that the Russian government will face serious consequences if there is an incursion.
In a statement, Foreign Secretary Liz Truss said: "The information being released today shines a light on the extent of Russian activity designed to subvert Ukraine, and is an insight into Kremlin thinking.
"Russia must de-escalate, end its campaigns of aggression and disinformation, and pursue a path of diplomacy.