Machine-gunners took up position outside the Crimean parliamentRussia's upper house of parliament has approved President Putin's request for Russian forces to be used in Ukraine, bbc reports.
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.
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.
Unidentified soldiers are guarding key installations in CrimeaThe BBC's Richard Galpin in Moscow says it is potentially significant that the request was for deployment in Ukraine as a whole, and not specifically for flash-points such as Crimea.
The upper house went into a special session almost immediately after Mr Putin made the request, in what seems to have been a carefully co-ordinated series of events during the day
Earlier, the lower house of parliament had urged the president to take whatever measures were necessary to "stabilise" the situation in Crimea.
During the upper house debate, one legislator accused US President Barack Obama of crossing "a red line" with his comments that there would be costs if Russia intervened militarily in Ukraine.
The upper house has recommended that the Russian ambassador the US should be recalled, although the decision lies with Mr Putin.
In Donetsk, thousands of pro-Russian demonstrators rallied outside regional government officesThe request follow days of military activity in Crimea during which unidentified armed men moved in to take over the regional parliament, state television and telecommunications hubs.
Soldiers from Russia's Black Sea Fleet, which is based in Crimea, are reported to be guarding some administrative buildings and military bases.
Amid the closure of airspace over Crimea's regional capital Simferopol on Friday evening, there were unconfirmed reports that Russian planes were flying in thousands of troops.
Ukrainian Defence Minister Ihor Tenyukh said on Saturday there are now an extra 6,000 Russian troops in Crimea, alongside an additional 30 armoured vehicles.
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