Russia's parliament today gave President Vladimir Putin the go-ahead to send troops into Ukraine, despite a warning from Washington that such a deployment would results in "costs" for Moscow.
Putin's request was approved unanimously.
The stark escalation of the ex-Soviet country's three-month political crisis came amid growing instability in Ukraine's predominantly Russian peninsula of Crimea that has housed Kremlin navies for nearly 250 years.
Large swathes of the rugged Black Sea peninsula of nearly two million people are now under the control of pro-Kremlin militia who have hoisted the Russian flag over the region's government buildings and seized control of airports as well as television centres.
Putin had remained silent since Ukraine's parliament ousted pro-Kremlin president Viktor Yanukovych on February 22 and then appointed a new pro-Western government that aims to move the ex-Soviet nation of 46 million closer to the European Union.
But the Kremlin said in a statement today that Putin had asked Russia's upper house of parliament to authorise the use of force in Ukraine until the political situation there "normalised".
"In connection with the extraordinary situation in Ukraine and the threat to the lives of Russian citizens... I submit to the Federation Council a request to use the armed forces of the Russian Federation on Ukrainian territory until the normalisation of the political situation in that country," the Kremlin quoted Putin as saying in the document.
Putin said that Russia also had to protect servicemen from its Black Sea Fleet which is based on the Ukrainian Black Sea peninsula of Crimea "fully in line with an international accord".
The Federation Council unanimously approved Putin's requested a lightning-fast debate.
Upper chamber chair Valentina Matviyenko also ordered the Council's foreign affairs committee to ask Putin to recall the Russian ambassador from the United States.
There was no immediate indication about the number of troops Putin intended to send.