“This is a major defeat,” said a senior Kremlin adviser, adding that the events of the last 24 hours bitterly remind Russian officials of the 2004 Orange Revolution, when Mr. Yanukovych saw his fraud-tainted election victory overturned after massive street protests brought a pro-western government to power.

“We made the same mistakes again” this time, said the Kremlin adviser, who spoke on condition of anonymity. “For us, the conclusion is that the West succeeded in engineering a coup d’état.”

Just what Russia’s reaction to this apparent setback would be wasn’t immediately clear. Western officials seemed to be going out of their way not to provoke Moscow. Some Kremlin aides in recent weeks had suggested Moscow could intervene to protect pro-Russian regions if Ukraine were to slide into civil war, but there is been no indication of high-level Kremlin support for such a move.

A pro-European government in Kiev, however, could find itself under heavy economic pressure from the Russians, who are a major fuel supplier and trade partner. “They have a lot of economic levers they can pull,” said Steven Pifer, a former U.S. ambassador to Kiev.