Pro-Russia lawmakers said they would also put the question of secession from Ukraine to a referendum on March 16, as the worst East-West crisis since the Cold War deepened with Russian forces maintaining their grip on the region.
The motion was passed by 78 out of 86 MPs in favour and was immediately condemned by Ukrainian authorities as "illegitimate", while the large ethnic Tatar minority in the Black Sea peninsula said they would boycott the vote.
A spokeswoman for the Organization for Security and Co-operation in Europe, Natacha Rajakovic, said they were "prevented from entering Crimean territory" and would stay in a hotel in nearby Kherson to "decide on next steps".
A Western diplomatic source said that the gunmen, who did not identify themselves, were "very professional, very well-trained -- this was not some militia".
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Wider diplomatic efforts to defuse the crisis also appeared to stall, with a second round of talks between US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov in two days ending with no agreement.
The measures were "in response to Russia's ongoing violation of Ukraine's sovereignty," the White House said.
European Union leaders at a hastily convened emergency summit in Brussels also pushed for Russia to opt for dialogue and de-escalation, while warning that sanctions were in the offing should Moscow refuse a diplomatic solution.
"We have got to make sure we get Russia and Ukraine talking to each other," said British Prime Minister David Cameron.