Members of Crimea's regional parliament have voted unanimously to make Crimea part of Russia, in an escalation of the crisis of the Ukrainian Black Sea peninsula.
The Moscow-backed government plans to hold a referendum on the decision on 16 March and the majority Russian-speaking population in Crimea is expected to approve it.
The sudden acceleration of moves to bring Crimea, which has an ethnic Russian majority and has effectively been seized by Russian forces, formally under Moscow's rule
Russian troops and pro-Russian forces are effectively in control of Crimea, a region whose population is mostly ethnic Russian and which has been at the centre of tensions following the fall of Ukraine's pro-Moscow president.
Ukrain's interim prime minister Arseny Yatseniuk said the decision was illegitimate, and Crimea was, and would remain, an integral part of Ukraine.
The Crimean parliament resolved "to enter into the Russian Federation with the rights of a subject of the Russian Federation" and said it had asked Russian President Vladimir Putin to start the procedure.
The Kremlin said President Putin was aware of developments but no response has yet been made.
The announcement from Crimea's parliament came as European Union leaders met in Brussels to discuss how to respond to Russia's troop deployment on Ukrainian soil.
The 28-nation EU condemned Russian actions in Crimea as illegal, voiced support for Ukraine's territorial integrity but took only minor steps suspending talks with Moscow on visas and a new investment pact, Reuters reports. The bloc warned of tougher steps if there is no negotiated solution within a short period.
By contrast, US President Barack Obama announced immediate first steps to punish Russians and Ukrainians involved in what he called "threatening the sovereignty and territorial integrity of Ukraine", ordering the freezing of their US assets and a ban on travel to the United States.