Russian President Vladimir Putin has ordered an urgent drill to check the combat readiness of the armed forces in western and central Russia, including areas near the border with Ukraine.
Defense Minister Sergei Shoigu says the drill will involve army, navy and air force troops and will check the force's "readiness to deal with crisis situations that threaten the nation's military security."
The announcement Wednesday comes as pro-Russia demonstrators faced off with supporters of Ukraine's new pro-Western interim leaders in the southern city of Simferopol.
Small-scale clashes broke out between the shouting protesters, some of whom were injured in the incident, which happened in the courtyard of an administrative building in the Crimean capital.
The Crimean peninsula is mainly made up of Russian speakers who support Moscow, though it also includes a minority Tatar group that tends to take an anti-Russia stance.
The Russian navy's Black Sea Fleet is based on the Crimean coast, and Russia's RIA Novosti state news agency Wednesday quoted Shoigu as saying Moscow is "carefully watching what is happening in Crimea" and taking measures to "guarantee the safety" of the fleet's "facilities, infrastructure and arsenals."
There are concerns Ukraine, a nation of 46 million people, could face an East-West divide after weeks of widespread protests prompted the ouster of Russia-friendly President Viktor Yanukovych.
Russia's Foreign Ministry on Wednesday issued the latest in a series of statements expressing concern over developments in Ukraine. It accused "extremists" there of "imposing their will and implanting their own rules," and claimed priests of the Russian Orthodox Church in Ukraine have been threatened with violence. The ministry warned these developments could lead to "an even bigger split in Ukrainian society."
Russia has said it has no plans to move militarily into Ukraine.
U.S. Secretary of State John Kerry on Tuesday said the country should not be forced to choose between Moscow, its former Soviet master, and Washington.
"This is not a zero-sum game, it is not a West versus East, it should not be. It is not a Russia or the United States or other choices, this is about the people of Ukraine and Ukrainians making their choice about their future and we want to work with Russia, with other countries, with everybody available, to make sure this is peaceful from this day forward because obviously, the terrible violence that took place in the Maidan was a shock to everybody in the world."
Anti-government demonstrations erupted in Ukraine after Mr. Yanukovych rejected an European Union trade deal in favor of economic assistance from Russia. The violence escalated last week with dozens of people killed.
On Wednesday, Ukraine's interim leaders dissolved an elite security force accused of carrying out deadly attacks on protesters during the demonstrations.
In a statement on his Facebook page, acting Interior Minister Arsen Avakov said he signed a decree disbanding the feared Berkut riot police.
Meanwhile, interim President Oleksandr Turchynov warned Tuesday in parliament that there are "very dangerous signs of separatism" in several parts of the country.
It is also unclear how Russia will react to the ouster of its ally. Moscow on Tuesday insisted it will not interfere in Ukrainian politics. Foreign Minister Sergei Lavrov said it is "dangerous and counterproductive" to force the country into a choice between Russia and Europe.
Mr. Turchynov plans on Thursday to announce a new national unity government.
The move comes EU and U.S. leaders meet with Ukrainian leaders to work on ways that Western financial institutions can help Ukraine, which many say is on the verge of economic collapse.