SIMFEROPOL, Ukraine — With cries of “Allahu akbar,” Arabic for “God is great,” thousands of protesters in the capital of Ukraine’s Crimea region, a tinderbox of ethnic, religious and political divisions, added an Islamic voice on Wednesday to the tumultuous struggle for Ukraine that last weekend drove the president from power and that has pushed Russia and the West into a face-off reminiscent of the Cold War.

Eight hundred miles away, President Vladimir V. Putin of Russia was ordering a surprise military exercise of ground and air forces on Ukraine’s doorstep on Wednesday, adding to the tensions with Europe and the United States and underscoring his intention to keep the country in Moscow’s orbit.

Taken together, the two events illustrated the continuing challenges that the new government in Kiev faces in calming separatism at home and placating a frustrated Russian leader who sees Ukraine as a vital part of his strategy of rebuilding Russian influence along the lines not of the former Soviet Union but of the czars. While few analysts expected a Russian military intervention in Ukraine, most said Mr. Putin was likely to respond in some fashion to such a stinging geopolitical defeat.

The question was how, and on Wednesday he provided a first answer, when Russia’s military put tens of thousands of troops in western Russia on alert at 2 p.m. for an exercise scheduled to last until March 3. The minister of defense, Sergei K. Shoigu, also announced unspecified measures to tighten security at the headquarters of Russia’s Black Sea Fleet on the Crimean Peninsula.