Russian armed forces are to be deployed in the Crimea region of Ukraine Valdimir Putin won the support of his country's Parliament for the mission.
Russia's upper house of parliament voted unanimously in favour of the President's proposed use of "the armed forces of the Russian Federation".
The move will continue until the "normalisation of the socio-political situation" in Ukraine, according to the proposal put forward by Mr Putin, and will take effect immediately.
Saturday's unanimous vote formalized what Ukrainian officials described as an ongoing deployment of Russian troops in the strategic region, and also raised the possibility that Moscow could send its military elsewhere in Ukraine.
Putin's call came as pro-Russian demonstrations broke out in Ukraine's Russian-speaking east, where protesters raised Russian flags and beat up supporters of the new Ukrainian government.
Russia's move sharply raised the stakes in the conflict following the ouster of Ukraine's pro-Russian president last week by a protest movement aimed at turning Ukraine toward the European Union and away from Russia. President Barack Obama warned Moscow on Friday "there will be costs" if Russia intervenes militarily.
