Ukrainian soldiers have been blockaded in their barracks in Crimea by pro-Russian troops
MPs in Crimea have asked Moscow to allow the southern Ukrainian region to become part of the Russian Federation.
Parliament said if its request was granted, Crimean citizens could give their view in a referendum on 16 March.
A government minister in Kiev said it would be unconstitutional for Crimea to join Russia.
Crimea, a region whose population is mostly ethnic Russian, has been at the centre of tensions following the fall of Ukraine’s pro-Moscow president.
Pro-Russian and Russian forces have been in de facto control of the peninsula, which already enjoys a degree of autonomy from Kiev, for several days.
The announcement from Crimea’s parliament comes as EU leaders meet in Brussels to discuss how to respond to Russia’s troop deployment on Ukrainian soil.
The Crimean parliament resolved “to enter into the Russian Federation with the rights of a subject of the Russian Federation”.
In a statement on its website, parliament said it had asked Russian President Vladimir Putin “to start the procedure” of formally allowing Crimea to join the Russian Federation.
The Kremlin said President Putin was aware of developments in the Crimean parliament, but no response has yet been made public.
If Russia agrees to Crimea’s request, the Crimean people will be asked two questions in the 16 March referendum, the statement says
• Are you in favour of reuniting Crimea with Russia as a subject of the Russian Federation?
• Are you in favour of retaining the status of Crimea as part of Ukraine?
Ukraine’s interim Economy Minister Pavlo Sheremeta, speaking in Kiev soon after the announcement, said: “We’re not working out what to do if Crimea joins the Russian Federation because we believe it’s unconstitutional.”
The move by Crimea’s parliament will significantly increase tensions as Western diplomats try to draw political leaders in Ukraine and Russia into negotiations to prevent a full Russian invasion of Ukraine, the BBC’s Richard Galpin reports from Moscow.