Russia’s upper house of parliament has approved President Putin’s request for Russian forces to be used in Ukraine.
He had asked that Russian forces be used “until the normalisation of the political situation in the country”.
Russia’s Black Sea Fleet is based in the Ukrainian region of Crimea, where many ethnic Russians live.
Kiev has reacted angrily to days of military movements in Crimea, accusing Moscow of trying to provoke the new government into an armed conflict.
Interim President Olexander Turchynov has called an emergency session of his security chiefs.
Meanwhile, big pro-Russian rallies have been held in several Ukrainian cities outside Crimea.
Russia’s Vladimir Putin submitted the request for troops “in connection with the extraordinary situation in Ukraine and the threat to the lives of Russian citizens”, the Kremlin said.
The upper house went into a special session almost immediately after Mr Putin made the request, and swiftly approved it.
Deputy Foreign Minister Grigory Karasin said, however, that this “does not mean that this right will be used quickly” to deploy troops.