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.
Meanwhile, Washington says it is issuing visa restrictions against a number of Ukrainian and Russian officials and individuals in line with a policy “to deny visas to those responsible for or complicit in threatening the sovereignty and territorial integrity of Ukraine”.
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.
“This means we have reunited with our motherland which we have been a part of for so long,” said Crimea’s deputy parliamentary speaker, Sergei Tsekov.
The Kremlin said President Putin was aware of developments in the Crimean parliament, but no response has yet been made public. Tsekov told reporters he believed most Crimeans would be happy about parliament’s move and would “support our decision at the referendum”.
Ukraine’s new interim government does not recognise the leadership in Crimea – which was sworn in at an emergency session while the building was under siege from pro-Russian armed men last week.
A spokeswoman for Acting President Olexander Turchynov said those in charge in Crimea “are forced to work under the barrel of a gun and all their decisions are dictated by fear and are illegal”. Interim Economy Minister Pavlo Sheremeta said it would be unconstitutional for Crimea to join the Russian Federation. According to Article 73 of the Ukraine constitution, “alterations to the territory of Ukraine shall be resolved exclusively by an all-Ukrainian referendum”.
But Crimea’s deputy prime minister, Rustam Temirgaliev, dismissed the suggestion, saying Crimea views the new authorities in Kiev as illegitimate.
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.
Ukraine’s new interim Prime Minister Arseniy Yatsenyuk met the 28 EU leaders before their emergency meeting in Brussels. Kiev, he said, was seeking a political solution, so “it depends on Russia, whether Russia is ready to fix this conflict”.
Some EU members, particularly those from Eastern Europe, have been calling for tough sanctions on Russia, while others – led by Germany – prefer to go down the route of mediation.
Both US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov are in Rome for a long-planned conference on Libya, but it is thought they may continue their discussions on Ukraine.
The two met in Paris on Wednesday, along with some EU leaders, in talks that Kerry described as “tough”.
Pro-Russian gunmen moved in to seize strategic sites in Crimea after Viktor Yanukovych was ousted as the president of Ukraine following months of protests in Kiev.
The demonstrations – by Ukrainians seeking closer ties with the West – turned violent in mid-February with more than 90 people killed in clashes with police.
