Britain Says Moscow Is Plotting to Install a Pro-Russian Leader in Ukraine

In a highly unusual public statement, backed by U.S. officials, London named the putative head of a potential puppet government but few other details.

KYIV — The British government said Saturday that the Kremlin was developing plans to install a pro-Russian leader in Ukraine — and had already chosen a potential candidate — as President Vladimir V. Putin weighs whether to order the Russian forces amassed on Ukraine’s border to attack.

The highly unusual public communiqué by the United Kingdom’s Foreign and Commonwealth Office, issued late at night in London, comes at a moment of high-stakes diplomacy between the Kremlin and the West. Russia has deployed more than 100,000 Russian troops on Ukraine’s borders that could, according to American officials, attack at any moment.

“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,” Liz Truss, Britain’s foreign secretary, said in a statement. “Russia must de-escalate, end its campaigns of aggression and disinformation, and pursue a path of diplomacy.”