A Crimean parliament official said voters will be asked two questions: should Crimea be part of the Russian Federation and should Crimea return to an earlier constitution (1992) that gave the region more autonomy?
"If there weren't constant threats from the current illegal Ukrainian authorities, maybe we would have taken a different path," deputy parliament speaker Sergei Tsekov told reporters outside the parliament building in Crimea's main city of Simferopol.
"I think there was an annexation of Crimea by Ukraine, if we are going to call things by their name. Because of this mood and feeling we took the decision to join Russia. I think we will feel much more comfortable there."
Russian Foreign Minister Sergei Lavrov, who had refused to meet his Ukrainian counterpart on Wednesday, had talks with U.S. Secretary of State John Kerry in Rome.
Earlier, Kerry also met his counterparts from Britain, Germany, Italy and France to discuss Ukraine and inform them of U.S. plans to sanction individuals and officials.
The White House said the order was "a flexible tool that will allow us to sanction those who are most directly involved in destabilizing Ukraine, including the military intervention in Crimea, and does not preclude further steps should the situation deteriorate."
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But the EU summit in Brussels seemed unlikely to adopt more than symbolic measures against Europe's biggest gas supplier, because neither industrial powerhouse Germany nor financial center Britain is keen to start down that road.
The short, informal EU summit will mostly be dedicated to displaying support for Ukraine's new pro-Western government, represented by Prime Minister Arseny Yatseniuk, who will attend even though Kiev is neither an EU member nor a recognized candidate for membership.